Good question.  I have some things I try to remember.

1) Is my board and gear all ready to use (waxed, binding bolts TIGHT, etc..)
2) Am I mentally ready (out to have a good time, nothing else on my mind)
3) Remember to drink plenty of water - even if not thirsty (makes a HUGE difference in performance)
4) Do I remember the basics and can I perform them on the first run (practice skidding and carving turns left and right, speed and direction in control before blasting down the mountain)
5) Remember how to fall correctly
6) Remember porper eye and skin protection

Thant's all I can think of at the moment.  I hope this is helpful to some people.