1) Don't worry too hard about making friends in freshers. Everyone is in the same boat as you, and people will go out of their way to be friendly in the first few days, especially if you're living in a flat.
2) Freshers friends come, and often go - I have a good 20 names in my phonebook of people I met in freshers who I've just fallen out of touch with completely, not deliberately but just a question of not seeing those people often enough and forming other friendships quicker. However, don't make the assumption that people will only be your friend until freshers then drop you when they've found their feet; while this may have some truth, the very first girl I met on the very first night is by far one of my closest friends.
3) Don't become trapped within your flat. All too often, people in a flat will just hang out with each other and not bother to move in wider circles, and after a few weeks a sort of cabin fever can ensue. You were put in a flat randomly with these other people, you can't be expected to get on and hang out with every single one. Try and make friends with people in other flats earlier on, before people get locked in their comfort zone.
4) As I mentioned earlier, it's pragmatic to anticipate there will be times when there is flat friction. Just try and be as flexible and considerate as you can be when you're living with others, especially when there's a large number of you. If you're living with someone you really can't stand, it's only a year. A flat is not a contract for any future housing plans.
5) People change - some who you meet in freshers are not the same by the time reading week hits. A lot of people see university as a fresh start and a chance to reinvent themselves. Sometimes this falls flat and they revert to a past self, or sometimes they find that the time from home and the new self reliance is doing them some good. Either way, by the time second semester hits, it's not unusual for friendships to both deepen and lessen
6) People are a lot more laid back at university. You want to go drinking 5 nights a week? Cool. You want to go study instead? Fine. You're a virgin? Nice. You want have sex with half the block? Go for it. You're a working class miner's son but want to take up ballet? Noone is stopping you. But just because people won't object doesn't meant they won't comment. Reputations can be easily built, but if you're happy in what you're doing, you'll get more respect for staying true to yourself and people will quickly come round to your way of thinking.
7) University recognises you are an adult. This can be a double edged sword. While there's not much stopping you going out, partying and skipping lectures, the university will not spoon feed you. Lectures can be very dry, with little interaction, and little to stop you zoning out. It is your responsibility to learn the material, lecturers only let you access it. People who come from private backgrounds can sometimes have a few adjustments issues because there's not as much 'spoon feeding' or contact time. In my course I have 500 other people with me, I'm lucky if the lecturer even glances at me.
Everyone hits a stumbling block at least once over the course of university, even if they don't show it. Some adapt better to the lifestyle than others, it's just how it is. Don't be arrogant - noone cares if you got 5 A*s at A level, chances are you're living with someone who got 6. Be gregarious, be relaxed, and roll with the punches. Seek out opportunities, don't expect them to find you. Invite yourself to friends events. Knock on a flatmate's closed door with a beer for them. Don't be afraid to be a nerd! People are paying 4 grand a year to study their subject, everyone is a nerd about their course to some extent. It's not an uncool thing to be excited about your course modules. Never again do you have the same freedom that 1st year gives you. You are living in an environment full of like-minded people, with little responsibility. Make it memorable.