It's been a long time since I've been to that particular concert (like 15 years long) but I will give you some general advice that works for most outdoor concerts. If the particular venue allows you to bring in water - do so, the day is long and it gets really hot. Make sure to bring cash for water - stay away from soda and energy drinks they will dehydrate you.
General safety stuff should go without saying but I'm going to say it anyway - don't go with random people (even if they tell you they know so in so in some band and can get you backstage). If you and your friend are tiny I would highly recommend staying out of the pit - you can easily get hurt, crowd surfing shouldn't be an issue (in regards to getting hurt) but I will tell you as a female I've been groped many a time while doing so - some accidentally and some on purpose. If at any time you are uncomfortable make them put you down (you can kinda force it by shifting your body position).
Also there will be multiple stages, kinda figure out who you want to see so you can make sure to head over to the correct stage at the correct time and what not. Way back when different bands would have booths set up - make sure to visit them, if they are still doing this it's a great way to score freebies.
Most of all just have fun, enjoy the music, and be safe!