support bras for the win, the more support the better, seriously, I'm an a cup and i used to come home with sore boobs
if you have long hair get someone to french braid it - two reasons, 1. it keeps it up out of the way 2. is a good protection from random crowd surfing boots at the back of the head
I second the cargo pants option, especially ones with fastenings on the pocket
wear really sturdy shoes, I used to wear doc marten boots, especially as that kept people off your toes (they were the oxblood colour, I wept when they finally gave up the ghost, seriously, I think I'd had them 12 years)
if you're wearing a band tee don't put another one under it - you'll swelter, a mosh pit is super hot
don't stand in front of the speaker if it's a heavy metal band - seriously, I was deaf for two days after bush at manchester
if the band throws water into the audience watch your head, as a little person elbows will get you then

if it gets too much allow the crowd to push you to the barricade they'll help you out, it's easier than going back into it
and flow with the crowd, the first time i went no one warned me of that and everyone got trampled at the start