Excellent choice!
Are you a Trolley-Dolly or a Trolley-Dave?
In either case, your first port of call is your local Navy Careers Office. Ring 029 20726813 (Cardiff office) and make an appointment to see somebody now.
Have you done it yet?...
...Well go and do it.... Now!
I see from your profile that you are 23. Rumour has it that the Fleet Air Arm age limit for pilots is moving into line with the RAF limit this year - i.e. you need to have actually started by your 24th birthday. It can take up to about a year to get in, so you might not have much time to spare.
Assuming you're not too late, the first step (after an initial interview with your careers officer) will be aptitude tests at RAF Cranwell. You will be called up for AIB if successful.
There are lots of fairly recent threads on the subject in this forum, so you may find it useful to search for them. It's all common sense though, really. The AFCO will give you information on what is required, so just make sure you do what they tell you. Make sure you're $h!t hot at mental arithmetic for the aptitudes and then learn what they tell you to learn for AIB (e.g. what all the different types of ships/aircraft do; what the RN does; who's the Foreign Secretary; where are the trouble spots in the world etc.)
Best of luck!
Pie