We do a night series here in Memphis. 3 races at a sports complex primarily made of softball and rugby fields. Unfortunately, the lights are rarely on during the races....
Glasses - if you don't have clear lenses for your riding glasses, get some inexpensive safety glasses from Home Depot. I race in some $10 3M safety glasses.
Pre-ride - Pre ride the course in daylight if possible. Find all the holes and ruts that will hide in the shadows when the sun goes down. If you don't, something will hit you just wrong during the race.
Lights - I like a helmet mount light better than a bar mount light. The bar mounted light got in the way, and flails around a bit during portages, whereas the helmet light 'goes where you point it'.
Clothing - watch the temps in the hourly forecast. Temps change fast at sunset!
Thanks guys! I've got the lenses, and will arrive plenty early for course recon. And I'll move the light from bar to helment.