How to meet lesbians?Watch
Other than that, people don't walk around with stickers on or stick to defined traits. You'll be more likely to find gay people on 'the scene' - in areas such as Soho in London etc - and clubs with gay nights/gay clubs, but not everyone who's gay will hang out in those places.
I'd imagine (if you're at uni) any LGBT societies are a good place to start beyond that.
The internet has a high proportion of people looking to experiment or, well, be a little more forward. You can usually harness that with sites like OKCupid, POF etc for dating or, I dunno, Craigslist if you're feeling a little more risque.
I met my Ex girlfriend on a social networking dating site thing.. however, it's usually easier to find someone through people/school/clubs/events you go too. (I met my current girlfriend of 2 1/2 years through high school/sixth form)
You can go on dating websites if that's your thing, or clubs - although sometimes people you meet at clubs are usually only looking for one thing when 'scouting' for people - it depends.
There's more Lesbians/bisexual girls out there then you think! It's just a means of finding them, (if you're looking for a fling, straight girls aren't always a 'straight')
Tumblr (if you're on it) is a great place to chat with lesbians - although most of them are dotted around the world (including London and England though!)
But yeah, specialist clubs,bars, and also support and/or activity groups should exist for this purpose if you live in a fairly large town. Try googling your place name+lesbian+the type of organised social gathering you want.