Hi there, Congratulations on getting airborne for the first time. Next stop will be your PPL, but above all, please enjoy the journey inbetween.
I am sure that there will be a lot of people who will pass on many hints and tips for you.
As for the books, Personally, I prefer the AFE range of manuals towards the PPL. They do not ramble on and on in great length, and are written in a way that is easy to understand.
http://www.flightstore.co.uk/prod/18...BOOKS/BKPPLUK/
When you get closer to starting your exams, the PPL Confuser will help you through all of the questions.

At 14 do not worry too much about the ground school side of thins, and don't go buying this that and the other.
simply
ENJOY YOUR FLYING