Choose subjects you enjoy, as long as you have decent grades in maths and science/physics GCSE, you should be alright. Dont go choosing subjects that you think are good for aviation but dont really enjoy, the two years of alevels will be a drag and pretty much $h*t. Trust me, i know! Go for subjects you enjoy and will excell in
Keep yourself involved in team activites. I decided that i didnt want to leave alevels and go straight into flight school, i much thought it was best for me to go university, doing cumputer science, something which i am enjoying. I have got involved in cricket, played to county level (not anymore, one bad match
), and also have a level one coaching cert, so i coach the youngsters at my club back in london.
As much as i want to be a pilot, wise words have been said, dont rush into things, and plan what you wish to do.
Good luck for the future and your alevels.