Hi,
Good luck with your application.
I bought a couple of books from WHSmith called Improve your IQ or Test your IQ. These help with the tests you will do at Cranwell.
As well as this, polish up your mental maths, especially speed / distance / time calculations as these come up very frequently.
Have a read about the history of current conflicts. You can buy books, but the BBC website is worth a few hours of perusal. Also keep an eye on the news and try to learn as much as you can about what is happening now in those conflicts.
And try to get hold of a history of the RAF book. They are available from WHSmith or AMazon, or if you know anyone in the RAF they were issued a year or two ago to everybody. AP3003 is the book you would need - it is an excellent history book. You may even find a copy on eBay. Haven't looked myself but it is the sort of thing which may come up now and again.
The careers people may even be able to lend you a copy if you are near to a CIO.
But the main thing is to be yourself in the interviews. I didn't know that much when I went in, and look at me now - I DRIVE the school bus!!