1) Carpool - Even if you're taking the bus, waiting in line is a lot more fun with friends. And there will be lines.
2) Set up camp - Decide what stage you will be in front of the most and stake your claim as soon as you arrive. Set up folding chairs and a blanket. You can always venture closer to the stage, but your home base will be there when you need it and everyone comes back to it eventually.
3) Bring binoculars - Best $25 I've ever spent. It's just you and the band in your own little up-close world.
4) Wander - You need to eat anyway and you're sure to hear some amazing music you didn't know you'd love.
As an aside, I advise the ladies tempted to wear platform heels (I saw several) to quiet that insane voice in your head and slip on some flip flops.
Not in Austin? Stream the festival (well, some of it) live... with only slightly annoying video latency.