The following link has a number of good fingering exercises:
precise fingering exercises?
I always stretch my fingers / wrists before playing. Curl the tips of the fingers forward (like a claw) then back. Curl the whole finger forward (like a fist) then back. Curl the hands forward (at the wrist) then back. Rotate the hands in a circle at the wrist. Do this again with the arms extended over your head. Stretch your shoulders too.
Also, another good stretching exercise is to roll the index and ring finger forward, and touch them with your thumb, extend the other two fingers, then release. Then, roll the middle finger and pinky finger forward, touch them with your thumb, extend the other two fingers, then release. Alternate a few times.
I've heard that some people like to soak their hands in warm water before a show. I dunno, I've never done this.
Hope this helps.