Heh, well I'll throw this in so u dont feel so insane.
I dunno if this is a superstition as much as its merely a habit but when I'm returning serve, I usually hold my racquet in my forehand grip while waiting. And as I'm waiting on the serve, I usually spin my racquet three times around going counterclockwise.
Its not that special but its just a little habit I have. Asdie from that, I've never had special boxers or a special shirt that I wear when I think I'm gonna win... lol course I usually DONT win so that's probably why hahaha. If I think of any other superstitious habits, I'll be sure to post um.