Don't Be a DickAll characters (and players) get this as their alignment - it's non-optional. You can play a "good guy" like a Paladin... as long as he's not a dick. You can play a "bad guy" like an Assassin or Warlock... as long as he's not a dick. You can play a money-grubbing mercenary... again, as long as he's not a dick.
What the boundaries of acceptable alignment behaviour are will depend on each group to a certain degree. If you're not sure if the other people you're gaming with would consider something within your character's alignment it's better to talk about it with them first. However, if you find yourself saying (or thinking) something like:
You probably know you were a dick and now you're hoping to blame it on your imaginary RPG character. Don't be a dick.
If you're feeling bored or impatient with the game and want to "get things going" by attacking the barmaid or trying to pickpocket one of the other player's character... don't. If you can imagine a hyper-active 9 year old disrupting a game with the same behaviour you might want to keep those impulses in check a bit better. Similarly, if you want to try and sort out emotional issues via roleplaying while your friends uncomfortably look on... don't. Talk to one of the camp counsellors instead.
With all the characters in an adventuring party now the same alignment you can have a wider range of classes and motivations for the PCs. They might not see eye-to-eye, and could even disagree with one another - but as long as none of them are dicks, everyone can have fun.