I don't make them all perfect copies or cut outs of myself, rather, I try to identify elements of my attitude that I would do. So I use anger or pride or whatever in my bad guys, and curiousity or honor or whatever in my good guys... Once I have that core in place, the character begins to act on their own. If I write something that doesn't seem like what the character would do, it seems wrong, it seems "out of character." Of course, if I feel my character is too flat, that means I haven't made them unique enough, or haven't challenged them or hurt them enough.
I think if you and your character share an unusual trait that this will help you present the unusual trait in a realistic way. I see nothing wrong with it.
I really don't understand the concept of a Mary Sue. It seems to me that it is a label readers apply to a character that they didn't like very much.
quote:
A Mary Sue is a character in a work of fiction who exists primarily for the purpose of wish-fulfillment on the part of the author. She plays a prominent role in the work, but she is notably devoid of flaws or a complex personality, and she usually represents the pinnacle of idealized perfection. All of the other characters love Mary Sue, because she is extraordinarily helpful, talented, beautiful, or unusual, and she often drives readers absolutely crazy because she is one-dimensional and too idealized to be realistic. The male equivalent of a Mary Sue is a Gary Stu.
And here is a test to see if your character is a Mary Sue:
http://www.springhole.net/quizzes/marysue.htm
This might have been posted before.
I ran across a lot of this when I was writing Internet Fan Fiction...lots of people would write themselves into the stories and interact with the characters. I avoided that (well, except for one oddball fragment of a scene I never did anything else with), but had the feeling that I could lay seventy percent of my life and attitude over the life of the lead character. Then again, I bestowed some of my life experiences on the characters.
I liked doing that, actually. I'd been doing it before, a little. I kept at it after returning to regular writing. To this day, I'll have something that happened to me happen to a character---
---but it doesn't mean that they're me.
But those are situations, not characters.
Though I have heard it said that Larry McMurtry always inserts himself somewhere in his novels. Maybe if it's just a small cameo it's not so bad.