Evil Party Members
I've never allowed evil characters into my groups. (At least in D&D, where alignment can matter.) Evil generally does not find constructive solutions to objectives/obstacles in my games. If the entire group was evil, then we could probably make it work, but I just don't have the heart to run such a game, typically.
In games with hard n' fast alignment rules, it's difficult. As soon as the majority learns about the presence of an evil character, they start planning for their sudden, yet inevitable betrayals.
I've had good luck with villain games, however. TSR's old Reverse Dungeon product started the itch, and Pinnacle's Necessary Evil made me realize that this was more than a one-time release valve for wannabe-heroes (despite some of the book's awkward morality). My current game, a Batman/new Changeling hybrid where everyone's a costumed villain of some sort. Then again, it could be argued that this is a game about selfish, villainous characters who aren't actually big-E Evil. Most of the time.
The two tricks that I use are same as any other game: making sure that there's space for personal and "quest" goals and reaching a common ground on tone. The goals give characters drive, shape 'em, and stop them from getting lost within the freedom of the fiction. Tone ensures that evil means the same thing to everyone, and they can function alongside each other even if the characters have squabbles.
I prefer my games to have characters that are reasonably like-minded, at least on the surface. The ability to work together is crucial. This is not to say they are forced to like each other, it's that they shouldn't be ready to point daggers at each others neck at the drop of a hat.
The key part in this quote, as I see it, is
on the surface. The samurai drama that I've been part of (L5R and The Mountain Witch) were all about characters who were bound by duty on the surface, but had human conflicts and mysterious pasts that tore them in all sorts of directions. Their straight-forward, typical adventurer challenges were always enough to keep them occupied and build bonds of teamwork, but the that only made the knives seem sharper when they did come out.