Hello I am just going to throw this up as if I were talking to myself. If you think it applies to you, blush really hard and then go practice and get over it. I just thought that anyone feeling new should benefit from two games worth of observed patterns and tics.
Survivor Etiquette
When in doubt, blow away Common Infected that are surrounding a friend as quickly as you can.
Any damage done to an incapped player will reset the "Help Them Up" timer. Any damage done to the Helper will not. They must be forcefully moved(attacked by SI, explosions, even a Boomer burst will do it.)
Expert Caveat: You must have doubt because friendly fire and 20 HP whacks are as bad as each other. But you will not play Expert if you can't aim, so.
Melee Expert Caveat: I've noticed that accidental melee swings are far less dangerous than accidental gun shots. Feel free to sweep one side(180 degrees) of him with an axe.
Gun Etiquette
Practice the Sniper Rifle extensively in easier difficulties or relaxed settings. Otherwise, get an Assault Rifle. The M6 in particular is almost perfectly accurate when stationary.
The AK is stronger than the M6. The M6 is the most accurate. The Short-Burst Army Rifle is an averaged choice.
Laser Sights do not benefit the Combat Shotgun, as it is intentionally made for wide shots. More than one Combat Shotgun may be a liability on higher difficulties.
The Grenade Launcher is not worth it at all if you are in any way remotely serious. Super Pros may be able to swing it just to show off!
Explosive Ammo is a colossal liability on Expert Mode.
Incendiary Ammo is always fantastic, but observe a difference in effect on targets. A Common Infected ignited will automatically die, lose it's hit-box and stop attacking anything. A Special Infected will persist unaffected with a DoT. The Tank will acquire a minor DoT that WILL wear off before it dies.
Grenades
Announce grenade intentions slightly before you do them to avoid redundant throws from multiple Survivors.
It is better to toss a grenade preemptively then to incap with it in your dipshit hand.
The Molotov produces an area of instant death to Common Infected. It is very hard to produce a "useless" molotov spread unless you misjudge which direction a Horde is attacking from. Special Infected burn until dead but are not impeded in function. The Tank will die in 30 seconds if hit by a molotov and does not require any further assistance in killing it. If a Tank is hit by a molotov, prioritize not being hit over shooting it.
Advanced Molotov Technique: If you are surrounded by CI and your friends aren't nearby, you can throw a molotov at your feet. It will instantly remove every nearby CI's hitbox and allow you to run, hopefully before the fire damage finishes what they started.
The Pipebomb will "wake up" Common Infected that are "asleep" and primarily attract Common Infected that are already active. In other words, Pipebombs work best when dealing with an active horde and are often disappointing when tossed into a new area "full" of sleeping CI. They will become aroused, take too long to reach it and come to a halt half-way towards it, falling back to "sleep" mode.
Pipebombs will not compete with nearby Biled survivors and often will not distract CI actively attacking a Survivor.
The Bilebomb provides the absolute longest distraction possible. Bilebombs will not compete cleanly with actual Biled survivors. Bilebombs will distract the Tank but this is sub-par compared to a Molotov and clean kiting. Bilebomb zombies gather into a tight cluster that can be easily gunned down, or even melee swept. If you forget about them, they will not forget about you when the bomb effect wears off.
Refining Aim
Always check your shots. There is no reason to ever shoot a man intentionally if you are not on realism. Spinning around to deal with a sudden situation and catching a guy in gunfire is OK. Hitting a dude because your shotgun or assault rifle sprays is OK. Putting three Sniper Rounds into a guy for walking into a door behind you is not cool. Putting a single slug into a guy's back because he is going to melee your trash zombies is not cool.
If you are on Expert, you check your shots because Friendly Fire is serious. If you are not on Expert, you check your shots because the Common Infected aren't so dangerous that you don't need to!
If a guy is REALLY firing(or hosing an area/horde rush), do not run in front of him except for the most dire of circumstances(shoving non-Charger SI, surviving a tough gauntlet, grabbing must-use bomb, etc.) It is not his fault if the second 10 of those 40 AK rounds hit you because you thought he was just pretending to shoot. He got the spot, he should be crouching, shoot over his head or side-by-side.
If you are on Advanced or Expert, you must prioritize crouching when possible if you know there are people behind you. If you are causing people to break the above rules, you are being a tool on point and may want to consider a lot of practice crouch-walking.
If you are incapped, you cannot friendly fire your teammates.
Point Conduct
Point is traditionally the target of most AI controlled Special Infected. You know the risks when you put on the Rambo Bandanna.
Point should readily attract trash attention and kill most garbage infected. Every one behind Point should not let zombies hit him from behind. He covers the front, you cover the sides, you cover his back.
Expert Point: Two guys with at least one melee and one shotgun, favor crouching over not crouching, the two behind should not be humping you but should hover close by. Maximum emphasis on not shooting your load over killing trash.
Health Conduct
If you get up from an incap and are Black and White, alert your friends. They can't tell unless they pay attention to the pick-up voice clip.
First Aid Kits are prioritized to "Black and White" Survivors.
You may plan around Defib use to subvert the above rule.
Use First Aid Kits as a preventative measure, not a repairing measure. You WILL be attacked within 20 seconds. Doubly important in Vs.
Pills give 50 temp HP. Adrenaline gives 25 temp HP.
Adrenaline lets you do anything with a "Time Meter" twice as fast. This is meaningful to recover from Tank near-wipes and similar multi-incap situations. It is even possible to help someone up while kiting a tank with practice.
Pills are the better choice if you are not familiar with or do not intend to specifically use Adrenaline. Adrenaline can make your controls feel "too lucid", and removes your ability to hear. Think of it as being unfamiliar with the Scout's excess speed.
Always communicate with your friends to plan around keeping alive. Again, heal before shit hits the fan, not during.
Common Infected
The easiest way to learn to deal with Common Infected is to practice with a Melee Weapon and a reliable "Primary Support" gun, i.e. Assault Rifle. Get used to taking a swing to kill everything in front of you and slightly to the sides, turning broadly, and sweeping again. Within 2-3 swings, you should clear any layer of zombies surrounding you.
Any Common Infected that strikes you will slow you down. As few as two can bring you to an effective halt.
Common Infected do 20 HP a swing on Expert. Any other difficulty it is wildly less. In VS, it is barely 2 HP a swing.
VS Priority is never being surrounded as a single person.
Expert Priority is destroying every Infected before it gets close enough to swing.
If you enter a new area and you see a bunch of idle zombies, these are usually Trash. They are distinct from Common Infected in that they are even easier to kill as they gradually "wake up", and cause a lot of cock-fighting where people hit each other trying to pad their scores.
Cleave a straight line through to a defensible point, keep an eye out for Special Infected, and clean out any stragglers that rush you from behind.
If you come to a halt in a defensible point and form a firing squad, be ready to temporarily reverse Point roles. Whoever is in front relative to the advancing commons crouches. Crouch in front, shoot overhead from the rear.
Do not ignore Common Infected. They become the most dangerous enemy in Expert and you are developing bad habits.
Do not ignore Common Infected hitting your friends. As long as you won't go ballistic and spray them with friendly fire, there is no reason not to help them clear off.
Common Infected should ideally be slain before they can begin melee swing animations, as 50% of these animations do not favor you hitting them before they hit you.
Do not stand near any spot where Common Infected can become "stuck", particularly above or below you. They can begin swinging automatically without animation.
Common Infected have their own sounds. Get used to them. You can become aware of when they've noticed you and "woken up." They will run at you shortly. You should be able to hear footsteps coming up behind you often. As in TF2 Heavy Play, you should have your mouse tuned to 180 effortlessly and deliver at least a shove.
Common Infected take a ridiculous number of shoves to kill. You can one-shot Trash(unaware, "asleep" CI) from behind, but this isn't L4D1 so don't bother.
When Common Infected die, they will not obstruct movement. Be sure you are not being hit from behind.
Special Infected
Survivors
Anyone actively being Special'd by a Special Infected is immune to friendly fire. Go fucking nuts on guys being crushed, pinned, choked and riden until they are freed.
The Charger cannot be shoved. Kill him with Guns or Melee.
Move horizontally away from a charge. Do not try to shoot him out of it "before" he gets to you.
Do not stand in spit to help someone up. Spit spreads from the impact spot. Get well clear of the area. When a Spitter dies, it produces a baby spot. If you melee a Spitter, keep moving away from the corpse.
The Jockey can be Shoved out of a ride, same as a Hunter pin.
The Boomer is not a race. If the Boomer has puked and missed his puke, he wants to hug you before you shoot him. You are not doing anyone a favor by making his dream come true. Shove him and immediately hit him. Prepare to be covered anyway.
Shove Smoker Victims if you cannot immediately take out the Smoker. Do not intentionally shoot at the tongue if a good shove is available.
Sniping a Smoker with the Uzi takes an unusually long time and the Shove is usually preferable if possible.
If a Smoker tongues you at point blank on level terrain, you may be able to shove him.
Shove Hunters if close. Shoot Hunters if not close. Stopping the Hunter's Pin is priority. When a Hunter pins a victim, he will shred them from full to incap to dead at the fastest possible rate. In comparison, a Smoker will do the same half as fast, a Charger will do the same a bit slower, and a Jockey will break off his ride at the Incap.
You cannot intentionally win a Melee "Race" against a pouncing Hunter or charging Charger. If it's in your hands and it's down to the second, by all means try, but do not bait such situations with false bravado.
Vs
The Charger is split between Offense and Support. If there is no chaos, he is a decent choice for starting it. If there is chaos, he is ideal for removing a green survivor from his friends. Especially if they must travel to that friend.
Remember that you charge until you would otherwise stop. The Charger is a very effective reverse Smoker for distancing Survivors.
It is better to charge at point-blank than to try and aim "Miracle" Charges that make you feel good.
The Spitter cannot move for a few seconds after spitting. This is why you "suddenly" die after your first spit. Practice spitting from hard to see spots or odd angles. It is worth dying to land a crucial spit. The Spitter is not made for Dick-Punching and recharges faster than the Boomer. It is better to stay alive and continually provide spit. Or in other words, do not suicide even against alert Survivors, but spit until it sticks.
The Jockey is almost entirely support. He works best in removing someone when everything else is going wrong(Tank attack, recovering an Incap, Boomer attack.)
If you ride a Survivor closer to the end of a level, they will get points until they incap. Don't let this stop you from taking an opportunity to get a good ride, though. Just be aware that if you have a choice of forward or back, you want to go back.
The Boomer's Puke is effectively melee range. His Death Boom is ridiculously wide and often bends space and time around terrain. The Puke is far less forgiving for anything being in the way.
The Boomer's Puke SWEEPS. It is a continuous stream, albeit a 1-2 second long one. If you are in melee range of two Survivors who are 90 degrees apart, tag one and swivel your mouse! You just might hit the other!
The Boomer is the most common wipe starter. He is best used in "Lose-Lose" scenarios. Sharp corners, dropping onto the ground, etc. Ideally, a Boomer should be seen as he's puking on someone and not before he is in melee range. Beware of walls that Survivors may shoot through.
For The Boomer, It is possible to cross a clear expanse of open air and reach melee, but do not assume you are meant to.
The Smoker is almost entirely support. He has a better chance of tagging and harassing stragglers and surviving than most. This is best done from behind.
The Hunter works best as support but may function as offense. His offense relies on being good enough to land damaging pounces or on being sly enough to inflict hits before he is killed. Pouncing a single Survivor when all three will kill you before damage occurs is a waste.
Killing Survivors
Any Survivor who is skilled with the Sniper Rifle will be a curse unto your Zombie House. Yes, they CAN aim that fast and reliably across open space.
The Special Infected must work as a team. Spawning one at a time and seeing if you can hurt somebody is a slow but steady loss. Coordinate multi-faceted attacks every chance you can.
When you attack is often defined by role and situation. In various situations, any Special Infected can begin chaos. In practical play, it is usually up to the Boomer and sometimes the Charger or Spitter to get things rolling. Most other SI will be instantly killed if identified, and usually instantly killed when immobilized in their Special Animation upon a victim.
Several levels are long enough that you will have multiple opportunities to produce a perfect incap. Patience is generally rewarded. When in doubt, wait for a Horde. Suicidal or Lone Dog behavior results in perpetually being a man down due to that 20 second respawn.
What makes the Boomer function so well as chaos starter is that biled Survivors cannot see the "shoot this red blob here to save your friend" outlines at all.
Coordinate, Coordinate, Coordinate.
Hunters, Jockeys, Chargers and Smokers can interrupt each other(though they will usually only bone the Smoker.) This is why you coordinate. It is better to call for a Jockey to finish a Survivor off than to apologize for breaking a perfectly fatal tongue.
It is better to lose Tank control to frustration than to play a bad Tank. But typically you are not afforded much chance to practice, so this only applies if you find yourself in a truly insurmountable situation.
Tank Conduct
If the Tank is lit on fire by a Molotov, he will automatically die within 30 seconds. All you have to do is kite him. He does not need to be shot to speed up the process, he cannot out-run a Survivor above 40 HP, and his rocks are not magical homing projectiles. Let him burn out. The only exception is if he actually submerges himself and puts the fire out, which is a super rare thing short of habitual Swamp Fever play.
The Tank moves slightly slower than a non-limping survivor. This can be further abused by proper kiting. Forcing the Tank to go around things in wide corners or to constantly change height levels will slow it further.
When the Tank throws a rock, either take cover(and stand a bit behind that cover so as to not test how accurate the impact physics feel like being) or be prepared to dodge. An AI Tank will track you until the very second it actually throws the rock. Once the rock is thrown, it is a straight line projectile. You will get hit if you try to run or strafe the entire time. Sudden changes in direction should do the trick, ideally when the rock is thrown.
If you are not limping, there is no reason to be hit by a Tank short of getting stuck on terrain or bad luck in trying to gun it down without a Molotov.
The Witch
Day Witches have a hilariously small aggro radius, but wide patrols.
You cannot crown the Witch on any difficulty above normal.
You cannot crown the Witch on any difficulty above normal.
You cannot crown the Witch on any difficulty above normal.
You cannot crown the Witch on any difficulty above normal.
You cannot crown the Witch on any difficulty above normal.
If you are not playing VS, avoiding the Witch is the default plan.
If the Witch cannot be avoided and you are not on Expert(or have a Defib), have your weakest member provoke it.
Be aware that if the Witch is provoked and THEN lit on fire by a different source, it may incap the different source instead.
Lighting the Witch on fire can help with a clean kill but is not necessary, particularly if the Survivors are competent in aim.
In a VS situation, the Witch is a highly interesting variable that the Special Infected should capitalize upon immediately, because the best Survivor etiquette is to get as far away from it as possible. Do not assume you will not be carried back to her if at all possible.