John over at The Mighty Atom has some good advice. Reproduced here:
Connected: The character has relationships (positive and negative) with other significant characters in the situation.
Committed: The character has a stake in the outcome of the situation, and will stay to see it through.
Capable: The character has the capacity to affect change in the situation by taking decisive action.
Conflicted: The character has beliefs and goals that are in conflict. They must make choices about which are more important, and which must be abandoned or changed.
Also, Gregor Hutton has some great advice in 3:16:
PLAY, DON’T WORK
Play is fun, so embrace the kill-happy machismo [this particular point is specific to the game. –Kit] and play with it. It’s not work, right? You shouldn’t be stressing over this.
LIVE THE MOMENT
Each moment might be your character’s last, so don’t try and plan ahead. Events and dice rolls will throw you a curveball all the time. You’ll find that the bigger picture will take care of itself in play.
BE A TEAM PLAYER
Listen to your other players at least as much as you speak. Do share your ideas but learn to enjoy the contributions of others too.
DON’T TRY TO BE TOO CLEVER
If you spend all your time trying to be clever or bring in more twists and turns it’ll just be tiring. Instead, just go with the intuitive and obvious answers that pop into your head. Simple is best.
Trying to be subtle can be confusing, and trying to make a convoluted plan worse. Be straight to the heart of the matter.
Be open minded and honest about how you feel. That’s the way.