Don't take expensive items:
A pretty obvious one to start with, but I thought it's worth a bit of a mention. Obviously you want to take pictures but I don't think it's worth taking your phone, I'd take an old phone and use a cheap/old camera, although the quality won't be as good I wouldn't recommend walking around with a huge DSLR, it can easily get lost or stolen.
Be careful of who you trust:
This counts in all respects whether it's with drinks, your belongings or even in your tent. You have no idea who they are, although most probably are friendly don't trust anyone with something which could end up hurting you in the long run.
I know most people go to festivals to get 'trollied' and listen to fabulous music which is fine but do make sure you know where your drink is at all times, also don't split up from your friends because it's a dangerous thing at a festival especially if you're drinking you will loose where your tent is. Also make sure you are careful around your drink don't let anyone you don't know near it, in case of it being spiked.
Learn your location:
Finding your tent in the dark once you've had a bit to drink can often be a bit of task, it's often worth jotting down/remembering a few key things about where you are, e.g. what camping area, near this stage, next these coloured tents and what colour your own tent is. It's great to get a tent which stands out because then you're more likely to be able to find it;
Drink a lot of water during the day as it can be hot and there a lot of people around so it's worth keeping your fluids up and don't stay in the sun for too long!
Find out more about ways to keep safe at festivals from Cloudstix here