My parents live in Colorado at almost 10,000feet, so we are out there several times a year, hiking, climbing, biking, etc.
Here are a few of the things we do:

1. Lay off both alcohol and caffeine

2. stay hydrated

3. start taking an asprin several days before and continue while you are there/ Asprin actually ""thins your blood a little, and makes the oxygen transport easier.

4. Acclimatize slowly if you can! HA

Good luck at the race