Andy - Congrats! Here are a few thoughts that may be helpful....
play in a couple of "live" tournaments before the NHC.
Go to Vegas a few days early and get any gambling, wildness, etc., out of your system.
Handicap the races in advance
have the courage to bet on a few (very few...not as many as you think you need) longshots and more moderately priced horses
try to avoid a group/entourage approach to the trip unlesss they are all-in on handicapping the races
review all of the official rules and review them again so you know and follow those rules
relax
have fun