oooh... to be honest I seem to be different from you lot haha!
I get on with just about everyone in my year! lol I know everyone and I have like hundreds of really close mates, boys and girls! Of course, there is a couple of people who I hate though! lol
To be honest, I used to be a lot like you guys and never got invited out much or whatever, but I just decided to come out my shell, and instead of being all like 'OMG I'M WORRIED WHAT THEY WILL FINK OF ME IF I ACT LIKE DIS....' I was just myself! And I'm quite a loud person haha, but like I get on with just everyone and can talk to everyone easily.
I think you should honestly just start talking to people! It's really the easiest way, and it could maybe be difficult to make freinds out of school or that... so just be yourself and get talking to folk! ;p