The 800m is a balls out race.
Warm up until you feel loose, stretch thoroughly!
Drink small sips of water, about a bottle split between before and after the warmup..
I don't know how old you are, but I'm assuming middle school.. when I was in middle school I would take it out 32 for the first 200m, then hold through a 65.. then just spill out everything you have in that last quarter mile... (This is of course assuming you can run..)
If it's your first time just take it how it is, if you feel like you can beat everyone else in the race sit behind the second place guy because the kid that goes out in first usually kills himself off the first turn.. I'd say kick with about 300m to go, and then kill all you got in the last 150.
now if you're in high school.
29, 30, 31, 29 is a respectable attempt.
good luck. oh yeah, and if you don't puke after your race you didn't run fast enough.