From my mailbox: A writer described If you have to ask, you may be over-participating.
Keep your "head down" in class for a week or so... only answer if called on. Listen to your peers for that week -- I mean really listen, don't think of counter-arguments or clever retorts. In your head, categorize the comments they make as follows: helpful/responsive; helpful/tangential; unhelpful/tangential. In future, make sure your own comments fall mostly into the first category and occasionally into the second.
I am a fan of class participation; I do not think it makes you a gunner just because you contribute to the class discussion. But make sure you actually contribute something.
Remember, you can't make your reputation in law school by any single comment in class, but you can sure as hell break it. If you really want the rep as the smartest guy in the room, shut the heck up and ace the exams.