Keep it simple. only use numbers if they are of significant meaning to you. Ive always used my nickname and my baseball number for mine.
Just dont put a bunch of x's and use numbers as letters. looks absolutely retarded and noobish. A lot of scrubs have x's in their names as i have come to find out.
Pretty much what bmxdude said, and don't put 'ii' infront of it either like iiTaCtKIcZ iiSkIlLz or whatever, i see so many of them. I think people think they are going to much better at the game by PuTtInG ThAt ShIt In ThEiR NaMe. ???? No..