Roleplaying yourself
You can't completely help it. The characters you play will always seem to have something in common with you. I think that is one of the parts of "getting in to character." The more you get in to the mind of your character, the more your character gains some of your way of thinking and acting. I think it is like how a movie actor lends his voice and style to each role he plays.

A huge difference between an actor and a roleplayer is that the actor always knows the kinds of hardships and loss his character will face. If his character is going to die, he knows that from reading the script. So, when he plays the scene of the character dying he has already prepared for the death. When stuff happens that hurts the character, the player is bound to feel a bit of the characters pain. That's part of roleplaying. The actor does it to, but he had time to prepare for it.

Personally, I like playing tragic characters. When I was involved in my high school Drama department, I always went for the tragic parts and I am told that I did a very good job with those parts. Most of the roleplaying characters I make have some huge tragedy. I don't know why. I don't think I'm working through issues or anything like that. Maybe it's just that pain and suffering come easier for me or seem more real to me. Who knows?