OK, been there, got the T shirt. Few simple rules:
1. Tell no-one but your boss at work you are going to have a crack at it unless you really have to....some dudes can get a bit antsy about you wanting to get on this wagon.
2. Go to the Stn Ed centre and get everything they have on the subject (do they still have those?). They should have loads of paperwork etc.
3. English, Maths and one other were required. If you have 5 or more all the better. If you have other stuff like A Levels, NVQ's or Dip's - better still.
4. Get a secondary duty (or 2) and learn to love it, even though you won't.
5. Join lots of clubby things - especially ones outside. They like you if you have another life and have interests in diverse people and groups.
6. Place "Air-Clues" strategically in the lav. Read up on what senior officers have to say for quoting purposes (the fact that not even they know what they are talking about shouldn't dissuade you). Not too absorbant, but shows you care.
7. The usual reading up on current affairs with a military tinge. Go left of centre to show how "avant garde" a character you are.
8. Know other peoples business including your own, other trades, branches and services. Don't discount other branches as an option, especially if you like to look of them and they are known to be undermanned. Remember, they are looking for an officer first and a branch specialist second, so they don't mind if you have a reason for the switch.
9. Sporting action is good and offers you direct access to some mother lode quality referees.
10. Get practice interviews sorted - they ain't easy if you are not used to them. Otherwise, ask yourself questions and rehearse answers. Dunno what it's like now, but the P2 interview on-base was always harder than OASC (they don't want to look like an arse for sending OASC a tool for a candidate).
It's really the source, and a great laugh if you can crack it and get to Cranwell.
Enjoy.