To build on what TheGM is saying, work with your DM to give them (say, ME) an idea of how to define YOUR play style. What works for you? What do you want out of a game? Do you want to take a new direction with your character? Be preemptive. Don't suddenly play yourself as a CE murderer and then be surprised when everyone stares in shock and horror.
Understand the game before it starts; what is it about? What kind of situations am I going to get into? What specifics about this world do I need to know before the game begins? What races/classes are street legal, what isn't? If you're curious, ask why. Find out what the DMs style is - is she an epic storyteller, looking for a massive (3+ year) story arc, or is it a series of adventure vignettes which are more about treasure & monster bashing? Know your play style, and what you're getting into. Don't build a 14 page character history then be dissapointed because you're surrounded by hack & slashers. OTOH, don't throw some stats on a sheet then be cross-eyed when the DM writes your background for you.
H&Ser: Um... I made a fighter.
Epic DM: Cool, needed a fighter. Where's he from?
H&Ser: Eh... what?
Epic DM: From? Where's he from? Why is he a Fighter? Is he military? Personally trained by a mentor? Just that good?
H&Ser: Eh...
Epic DM: Okay. I'll write your background. Please note on your character sheet: "Plot chew toy."
You can easily imagine this going the other way. You've probably seen both scenarios. Friends don't let friends roll play in an Epic RPG.
Games are designed as cooperative story telling experiences, but your DM is writing over 50% of that material; be willing to give them feedback. "You did this, and it was awesome, this? Not so much." The DM is a player too, and many (like me) can have fragile egos. Working within the framework of the story to tell YOUR story is part of what makes the game so cool. So take advantage of the opportunity.
Remember that you are one of X total players, them having fun is as much your responsibility as the DMs, so don't do things that would detract from their entertainment. Yes, I left this intentionally broad and vague. Too many people can't handle it, and they can be great role players, but lousy gamers.
And, my favorite: don't rules lawyer with the DM mid-game. Abide the current ruling, make a note (eep! a note!) so you can refer back to it later and say "Hey, you've done this before, RAW says this, and I think this. Let's talk about it and agree on a consistent ruling."
My two cents.
LCpt. Thia Halmades