Acknowledge them, too. Some sessions have plenty of performers, but it's arguable that the ratio of listeners to players is a good measure of how good the session is. Don't go wandering off to the bar just at someone's 'big moment'. Treat them at least as well as you think they could possibly want to be treated. Especially newcomers and people you don't know.
Egos are fragile.
Be ever so careful about ribbing even those you think can take it. But don't take over. So long as the total enjoyment quotient of all is increased then that's what we should be aiming for. Don't out-perform the person who's performing. Maybe it's their first time.