I've not been but the reviews from last year were very positive. There hasn't been any serious violence for a few years (and possibly when it was at a different location).
My advice is the same as it would be for any large event such as this, keep your wits about you and your valuables hidden from view. If the atmosphere changes for the worse as the day turns into evening then don't wait around to see what happens, leave.
Make sure you know your nearest exit and know how you intend to travel home (i.e. where is the bus stop you need and where is the one two stops before it reaches the park).
These are some basic rules for how to be paranoid at a large event, and they are completely unnecessary in virtually all occasions. You can be more paranoid, but in the end you will have more fun if you stay at home with a blanket over your head.

I'm sure you will have a great time at the festival.