The best advice is what you are told do do during freshers. Be chatty, introduce yourself and act interested in their course/lives/etc. The first thing to get you talking to them would be asking which cupboard/ shelf is free for you to put your stuff (if you're self catered). If they're quite a close flat they'll probably all eat dinner at around the same time. Make sure you're in the kitchen then at least sometimes. Sit with them and talk, or if that's too daunting just try and chat while you're cooking. If you run into one of them in the hall/kitchen/outside always at least say hello.Personally, I'd be honest and say that you never got close with your first flatmates and you didn't feel at home. If they're half decent people they won't mind you joining in.
One of my flatmates switched flats into ours and she's so much happier here because we don't ignore her like her old flat did!