Apparently people like quick and easy posts with numbers, so while I still stray on the teal deer lines, here's something I whipped up from reading about a bazillion management articles this morning.
1) Really interact with the other PCs.
Seriously, even as a GM, ask questions of them: how, why, who ... and allow room for description. (And as a GM? TAKE NOTES. Don't be too quick to say, "But that wouldn't have happened in Takatakastan.") Same with NPCs; the more you ask, the more opportunity you have to flesh things out and make the game better for everyone.
2) Remember that everyone is better than you at something.
That's what the idea of not overlapping your niches is about... so let someone else's character shine at a scene. Better yet, help set them up to be awesome. If you know that the person who sits on the end makes great characters but is nervous playing them, can you prompt them a little?
3) Give positive feedback.
Compliment your fellow players on something they've done during the game that impressed you. Tell your GM about something that you liked about the game that you might want to see more of... Often we don't give feedback and the GM is just thinking, "They came back to play again. They laughed a lot. I guess I'm doing something right...?" As a GM? Ask what they liked about it, or what they learned from it.
4) Show a little vulnerability.
Quiet or at least argue with your inner voice when you're worried how you'll look at the table. Tell people, "Okay, this might be a stupid idea, but what if...?" Let your character fail, because that's going to be an awesome story. Ask the people around the table what your character should do in a similar situation.
5) Use all your resources.
Assume your opponents are smarter and better than you. Play to win, not just to deflect. Bring all your creativity: why are you still carrying that ten foot pole?
6) Don't insist on playing nice.
Imagine the worst that will happen. If we all "just get along," we become bland. Avoiding inconvenience and having everyone "be good" and "constantly aware of possible disparagement" is almost the same thing as ignoring what needs to be brought to attention.
Sometimes it seems there isn't a real objective criteria.
Sometimes that takes conflict in order to find the real boundaries. This isn't the same as suggesting people aren't responsible for their behavior.
Oh, and always brag about your mistakes. That way you remember them and they become a legend.