At its most basic Reading festival is like any other festival. ~80,000 in a few fields. Your fears about rioting and burning tents is somewhat warped - that happens at every major festival - but it's never malicious. Basically people get very high on all manner of sh*t and go nuts. They become selfish and don't really think about other people. I went to Reading in 2013 with my girlfriend and we had a minuscule little tent. We camped in Yellow 1 which was the centre of all the partying and we didn't encounter any aggression or d*ckheads trying to **** sh*t up. Even so, we didn't take anything we valued (phones and wallets locked up in locker) and we were very relaxed about random people parading through at 4AM every night. Go with a carefree attitude and you'll really enjoy it.
I think the main thing to remember about Reading is it's a festival for 'young' people. That's not to say that there aren't any older people there but there's a lot of teenagers and it gets crowded and can be uncomfortable near the stages and even while walking around the campsite when it's busy. Stick with your friends, keep in contact, learn how to get around (very important - the campsite is f*cking massive), look after your welfare needs and on Monday you'll be real sore that it's all over.
Libertah