First off, ignore all those
er's who try put you down.... no names mentioned.
Obviously, passing the tests is a big thing... however also fairly obvious.
You need to gather (and learn) as much information on the RAF, NATO, EU, MoD etcetc that you can find.
You need to practice interviews, leadership and teamworking as much as possible. If you're generally quite quiet, try doing as much public speaking as possible to build your confidence.
The fitness test is difficult, but as you say you do quite a bit of exercise, it shouldn't be a problem, although you may find it useful to practice bleep tests, press ups and sit-ups.... wearing kit.
Practice some problem solving exercises as they will be useful both in the aptitude tests and in the team ex's.
Keep up to date with current affairs, such as uk and worldwide events, politics, that sort of thing, and form you own ideas about them. Don't be swayed by media (or interviewer) pressure!!
Learn about yourself! As in, memorise important dates (use calender dates, not "in year 10 I....") and be prepared to boast a bit about what you've done and what you thought about it. Also think of things you would like to do and why.
Join lots of clubs/societies/ATC?/etc to show you are keen and well organised and motivated.
However, the main thing is to be 100% certain that the RAF is for you, and that you are the best thing for the RAF. Make sure you have reasons!
Not much then!!
I wish you much good luck, and please don't be put off by certain people to ask here (or anywhere) for help!
Matt