When you arrive just keep on walking about the site until you find a suitable place to camp. I suggest, if you can, to camp close by some kind of noticeable landmark. Camping near a pole, near a sign or near a path is a great idea. When you're trying to find your tent in the dark, you're drunk and there are loads of people wandering around...it's difficult! Go somewhere you think you'll be able to find when you're drunk, lost and it's dark. Ask some of the wardens (they wear green jackets and have a big number on their back) if they can tell you a good place to camp. We asked and they directed us to a place most people bypass. It was great, right by a big food place, near the toilets (they didn't smell!) and near a light. Great! Ask and you're more likely to get a good place.
When you're searching you'll be able to tell where is good and where isn't. Depending when you get there it'll most likely be full of tents near the entrance. Keep walking and don't bother about the campsite you're in, they're ALL noisy, all full of drunks and all impossible to sleep in. Green camp really isn't green.
To be honest, you'll be hard pushed to find two camping spots. It took us an hour and a half walking around with HEAVY bags to find space, finding another one would be annoying, but that's up to you. I wouldn't recommend leaving anything unattended. It's prime pickings for a thief. We used our clothes and stuff as a mattress. Not only did it reduce the chance it'd get stolen, but also kept us a bit more comfy.

You're free to walk around the campsites at your will, you can go wherever whenever.
Have fun! You'll get it all figured once you're there.
