Watering plants: the main problem I've found is that the water creates channels in the soil, which causes parts of the soil to remain dry, even after thoroughly watering plants. Two solutions to this: 1. aerate the soil using some kind of pointy object. This can be dangerous for the plant, especially if you don't know what you're doing. Since you're dealing with houseplants, you won't have much room for maneuvering, so I'd stick with option 2: soaking. Using a sink, or bathtub depending on the size/number of plants(I have a few dozen, so I have to use my tub), put the plants in the whatever, and fill it up to the top of the pot, but not over the top(or you'll have a mess.) Let the plants sit for a while, let the water out, then let them sit for a bit longer so they can drain. I wouldn't recommend this unless you have a pretty dry home, otherwise you'll have problems with mold.
Soil/pot changes: Most houseplants, you should change about once a year. Herbs, vegetable/flower bearing plants, 3-4 times per year. Make sure you put a small rock or shard of clay pot, just big enough to not fall out of the hole, over the hole in the bottom. This helps the soil drain excess water, and prevents root rot. Even if you don't repot the plant, you should still change the soil, and break up the root ball. Pull the plant out of the old pot, take it outside, and gently pick the root ball apart. Try not to damage the roots, but don't freak out if you do. Cut off any root sections that look diseased or dead. Make sure to note if your plant has a taproot(one large root as opposed to a bunch of little ones), as plants with taproots will need a pot that can accommodate the entire taproot without bunching up, plus room to grow.
When selecting a pot for a plant, pick something appropriate for the size, and variety. Most plants will do fine in a pot that's too big, but a cactus or succulent needs a pot that's just barely bigger than the plant. The exception to this is tall cacti. There's a specific way to calculate the pot size for a tall cactus, but I can't remember it right offhand. Unglazed clay pots are the best, as they don't hold moisture as long as glazed pots, but as long as your plant has adequate drainage, it should be ok. Never put a cactus in a glazed pot.
Feeding: I generally use half strength for whatever the instructions on the package say. Miracle-gro is fine, for cacti use the vegetable mix, again, HALF STRENGTH. It's better to underfeed your plants, than risk damaging them with too strong plant food. If you want to be all lolganic, buy some alfalfa pellets from a pet store, and scatter a small handful on the top of the soil. As you water the plant, the alfalfa will break down, and feed your plant. If you don't like the au natural look, you can leave about an inch on the top of the pot soil-free, and fill it up with rocks or gravel. No glass beads.
Sun: Unless the plant specifically needs shade or full sun, just assume partial sunlight. Any space that has enough natural light that you don't need a lamp, but isn't in direct sunlight should be fine. Depending on your plants needs, place it further away or closer to the window/door/whatever the light comes through. In case of full sun plants, be careful when introducing them to full sun, if they haven't been out in the sun wherever you got them from. Set them close to the window or whatever, and over time, move them closer to the sun, until you have them in full sun. Just like you, your plants can get sunburned. This can be fatal, and at the very least, it will make the burned part of your plant very ugly. This isn't such a problem in fast-growing plants, since the sunburned part will be replaced fairly quickly, but cacti and other sun-growing plants will most likely have those burns for the rest of their lives.
Other than that, just try to remember that plants are living things, and they need just as much care, or sometimes more, than others. Don't take on a plant that requires more care than you're able to provide.
Oh, and if you buy a cactus from a retail store, do yourself and the cactus a favor and take the goddamn straw flower off ASAP.