apply to halls with a known social scene if thats what youre into. youll find people who want to go out every week without the need to be forced into societies to make friends (cue LARA if you want a pissup, or, as ive just discovered on friday night, join the celtic society. the celts know how to drink, and i remember very little past my centurion...)
corridors rather than flats open things up and youll meet more people, even if your corridor is filled with unsociable people (ie mine, well most of them).
as nadinus said the AU is a super way to make friends and have a guaranteed social group, but if im honest, if i didnt join the AU i would have still found my core group of friends in my hall, none of whom are AU... but my AU mates are also awesome and some of the coolest people on earth, and it is the ideal way to get away from that assumed work-heavy-unsociable-crappy-place-known-as-lse-to-many.
id say i made the right decision with LSE. you arent expected to go out on the lash every night, but if you do, that's fine. if you have a heavy week of going out 4-5 times, fine. i like not feeling pressurised into going out every night just because im a fresher, which is awesome. There are means of being able to party HEAVILY in central london for cheap. Monday: Tiger, Tuesday, Pacha/ ministry of sound (i think, never been!), Wednesday: Zoo/Walkies, Thursday: Onanon, Friday: Crush (i was trashed on £15 and thats expensive), Saturday: Sports Cafe/Afterskool club (at lse). the means are there, definitely.
so to sum it up in 3 lines:
Accommodation: Corridored ones to maximise exposure to people and avoid the risk of crappy flatmates
Societies: anything that interests you, to get some friends. you dont have to go out on the lash, chat about politics or religion.
Least importantly: AU, if you love banter and playing sports. guaranteed friends, and to maximise potential for social, join rugby, football, hockey, netball. i think theyre the main ones. womens rugby is known for its massive turnout every week. we get 80-90% of the main team out alot, which is fantastic.