Just did my stage one today! Try and practice some spatial awareness tests using cube templates, and make sure you read the notes as recommended in the confirmation email. It is quite a relaxed affair, and the instructors are helpful. THe most important thing they stress is accuracy and speed. Most of the other candidates i talked to only managed to finish about 70% of the spatial awareness paper, so don't be alarmed by that.
Quick thankyou to the regular contributors on the other NATS thread, as their advice is invaluable, so make sure you read it!
oh, and good luck!