Every character has to be unique. Oh! I wanna be Luke Skywalker. No. It doesn't work that way. With each character you create, it's best to make him or her (or both or neither) believable enough and unique enough that you'd think George Lucas would actually put him/her/it in a Star Wars movie. You achieve optimum play when you do this. You can really get into character this way. Here's an example.

Say you're character is a pirate. A pirate wouldn't be timid, caring, or have a soft side of any kind. But he might have some kind of weakness. Maybe he's got a trick left knee that decides to go out on him every once in a while. He'd be very protective about it and be a little apprehensive about something that would mess up that knee any more. He also might blame anything that goes wrong for him on his knee. Or he might grit his teeth whenever his knee hurt, letting others around him worry about him. He'd do this to show how tough he is, warning them not to mess with him. He'd be selfish and greedy. He'd kill for money. Now THAT's a PIRATE.

Don't play a mean tough guy because it sounds cool and then turn him into a good-guy Jedi superhero. The personality doesn't fit. You might have to be prepared to play a weenie character. Once in a while the little guy wins too. And every group needs an oddball. It adds for more interaction between characters and more of a story and background to it. Conflict is good.