#01
Assess physical condition.
Hopefully the invitation will have arrived in plenty of time to enact a rigorous exercise regime if necessary. Head on over to your local 24 Hour Fitness ASAP.
#02
Crash Diet
It doesn't matter if you still have the body you did when you were 18, this is your high school reunion and these people haven't seen you in a decade. You need to look 16... at least for one night. It's totally unhealthy but crash diets will work for one night of glory.
#03
Get yourself to the salon.
Start making those appointments now. If you don't have the time to work it in the gym, and you lack the will power to diet, then at least groom yourself. Cover the gray, go back to blonde, or wax it off. Anyway you do it, make sure your hair is dressed to impress. Better get your nails done, while you're at it.
#07
Create an impressive back-story.
No one wants to here about your real life. To make the night more entertaining for you and everybody else, create a totally outrageous life for yourself. You can be an astronaut, a deep sea diver, or you could potentially be homeless (the fact that you received an invitation might discredit this one). Just be sure to stick to your story.
#08
Arrive in Style.
You know you don't want to show up to the reunion in your ten year old Volvo you just can't seem to part with, let alone wash. You could always buy a new car for the event, but this is not always feasible. The best, and most inexpensive, solution is to just rent a car, but make sure you splurge for the nice one.