I've only been to Paris, but I met a few fashion students at the shows, so maybe that would be an opportunity for you to explore. The basics are that you need to be of some use to the brand to be let in, either press, buyer or celeb. And the men's shows are a lot easier to get in to than the women's shows, with Dior Homme as the only real exception.
But really, seing a fashion show live ain't much. It's a lot of waiting and after ages you only get a very quick glance at the clothes. If you're in it for the clothes you might as well look at the pictures and videos posted here. If it clothes you want the showrooms are a lot better (and easier to get in to if you don't mind a bit of acting).
But if you're into trainspotting celebs you might be in for a treat...