I remember my freshers week like it was yesterday! OK, not all of it obviously, but the afternoons and the times we had in the flat after getting ready and after the night out.
Everyone's really friendly. There are plenty of reps there to help. Plenty of freebies. Plenty of alcohol. Lots of sex, too!
I drank a lot, I think. Not every night, though, as I knew if I did that then I simply wouldn't have lasted long. For some of the days I had early morning starts because of introductions etc., and I had heard horror stories of people getting vomited on by people too hungover and I didn't want to be one of those guys that got a rep for puking on people.
Generally, I just went to the organised nights out as they were the best and had the most amount of people there that were in the same boat as me in that they didn't know anyone else.
Don't try and get all pally with your flatmates if this means that you're losing out on opportunities to make other friends! Your flatmates will be there the entire year, but often friendship grounds form fairly quickly. Ironically, I mainly hung out with people from a totally different flat during freshers week but it wasn't long until my flatmates were my best friends.
And lastly, yeah, there's loads of sex. Almost everyone I knew got some 'action', so to speak. So if you want no strings attached sex, you'll get it. However, plenty of relationships formed out of freshers as well. Really easy to meet people of the opposite sex, and long distance relationships usually failed really early so if the person you have an eye on is taken, they'll probably be on the market pretty soon.