|festivals are fun, especially music festivals. as to what to do, it depends on who you're shooting for. if you aren't affiliated with anyone (ie, participant, production company, editorial agency, etc), then you're essentially shooting on spec and may have a limited market for what you shoot. most likely, you'll have a media pass which is typically better than a VIP pass but not as good as an all-access pass (which are usually reserved for people shooting for the event producers and main sponsors). this usually gets you in the pits, side stages, and sometimes access to green rooms.
if you are shooting on your own, your best bet is to cover the event as if you were hired by the company producing the event and to cover it as photojournalistically as possible. shoot to tell the story of the event, showing all the great times people had. capture all the things that make the event what it is. of course, shoot the main attractions, but also tell the rest of the story.
what this will get you is a portfolio collection that you can use to sell the event producers and/or sponsors on hiring you to be an officially affiliated photographer at future events. just don't throw them more than a bone or two because if then see what you can do for free then they can only imagine how much more you can do for free in the future. you really have to present yourself as a professional gun for hire, not just someone looking for credits. along those lines, avoid the urge to put all your best stuff on social media. cherry pick your work to highlight what you can do and tease people into contacting you for more.
one last note, along these lines. you will most likely capture stuff that the performers will want to get copies of for their website, marketing, etc, etc. keep in mind, these people are being paid to perform. they're professionals. they hate when people steal their music. they are *NOT* broke. the *CAN* afford to pay you. you just have to tell them that you'd love to work with them and that you have developed a solid reputation for treating your clients fairly when it comes to pricing your work.
have fun! should be lots of sites, sounds, and more than enough stuff to shoot.