What are you interested in, i.e. what do you do for fun?
There's an
old thread here which may give you some ideas
I'd say try and find what there is in your area and see if you fancy anything. Look around everywhere- not just the internet. Scour the public notice boards, the public library, cafe and pub flyers, bus stop flyers, gumtree ,and newspaper adverts (I answered a newspaper advert looking for a trombone player which has led to tons of opportunities and friendships for me). Also, don't be afraid to try things you haven't before, you never know what you may end up loving to do and what paths this may take you down.
Also, there is this
thread on making friends and I always enjoy the article posted in
this thread about making friends as an adult (because it really is like dating!)
For those folks who aren't really outgoing (I am really not outgoing or extroverted, I am very introverted and have introspective energy -I really have to force myself to be and use a lot of energy up for!! But when I'm doing something I love, I find the energy easier) - I always just say to myself, getting yourself over the line is the hardest part of trying something new. Once you're in, people will be welcoming and friendly and happy to have you there. If they're not, you don't want to be there anyways!!
Good luck!