All the advise above is good. Keep up with the current affairs and Naval knowledge. Also keep yourself fit.
As far as aptitude test go you can't really practice for them with the exception of mental arithmetic, especially speed, distance, time calculations.
Now is as good a time as any to join the RN as we are going to increase the numbers of pilots and observers we are recruiting. A stark contrast to the RAF!
Your ACLO has probably told you to come back later because he thinks you need some more time to learn your stuff. Use the time wisely.
800 NAS and 801 NAS will reform as GR7a/9a squadrons. The last SHAR course is coming to an end at the moment as 899 NAS will disband in March 05.
Don't hold your breath about being a fixed wing pilot in the Navy on your first go. Usually only one or two people in every two or three courses gets streamed FW at Barkston. A lot of those get chopped at Linton or Valley. However it is possible to be re-streamed fast jet at Shawbury at the end of 705. A guy from there started at Linton a few weeks ago (although it is not very common). There is also the AIR 309 course which is the fixed wing crossover. This is where most RN fast jet pilots come from.
Basically it is unlikely that you would be streamed FW after EFT but there are more opportunities later, that way you can have the benefit of having flown RW and FW.
Joe2812 if I were you I would apply to both. Especially if you are really serious about becoming a military pilot. If you are worried that in joing the FAA you might spend long periods at sea, you would probably be doing the same in the RAF anyway with Harriers or Chinooks! Why don't you ring your local RN careers office for information and see for yourself?
If you have anymore questions feel free to PM me.
Best of luck!
Jucky.