OUDS - the Oxford University Dramatic Society
Oxford University being organised into a system of colleges, there are opportunities for people to get involved in most hobbies at all levels. Start out by representing your college in the competitions known as Cuppers, which take place in most disciplines. If you get on well, you might represent the University team at your sport, or get involved at drama in one of the bigger theatres. Similarly in music there are chapel choirs at most colleges, then more prestigious university-wide groups in all musical genres. It's a good way to meet people outside your college or subject too.