As somebody mentioned above, they aren't expecting you to be an expert on ATC when you go for the tests and interviews. There's not a great deal you can do to prepare, except read the stuff they send you and just brush up on aircraft recognition. They are looking for generally calm and logical people (how the hell did I get in?) so stay cool and try to enjoy the experience!!!!!!
Best of luck to all those who are going through the selection tests. This job is sometimes frustrating, very occasionally terrifying, but mostly excellent fun!