I am currently between JEFTS and BFJT and have been in the service since April 2001. The advice already given has been spot on, know as much as possible about the RAF and its interests, you can never know too much IMHO!!
The guys at OASC need to assure themselves that you are worth the investment, especially as a pilot, so you can expect to be asked a lot of questions about the service that you are keen to join.
Some of the Q's I was asked during interview (I applied for DE pilot and nav) were along the lines of..."so you would like to fly the Eurofighter, in that case tell me the training path that you would take if you were to fly the C130..."
"How many engines does the Merlin have?...Why is this?
"So your first choice is pilot...how many hours will you fly on the Dominie during the advanced phase of navigator training?"
As a Direct Entrant, I am 20 years old and I have enrolled on the In Service Degree Scheme which I will not start until after my first tour. I was not a 'straight A student' by any stretch of the imagination but I was always prepared to work hard and do the Sports, charity work etc, which has helped me as far as I can see.
If you want any specific info,drop me a line and I will do my best to help you out. I have still not forgotten posting identical threads when I was going through the selection process and I was very grateful to the people who helped me at the time.