Hi there,
the first thing to do is apply for your licence, you can do this now but it won't be valid until your 17th birthday.
I don't think you can sit your theory test before then as you have to take your licence with you and you won't have one until you're 17 but you can do a lot of studying and prctice tests, there are several websites that do mock tests and it's probably worth investing in a CDrom of test questions and one of interactive hazard perception tests.
The quickest way to be ready tosit your first test would be through an intensive course (usualy one week) but this is normally quite an expensive route and does not give you as much expereince on the road as a block of lessons over a longer period (with lots of practice in between) would. It's also a greater dissapointment if you fail having spent all that money :(
You don't need a professional driving instructor but it is advisable as they are not teaching you to drive but to drive in the way the examinor is looking for on the test. It is unlikely your friends or relations will be able to teach you all the things you need to know fro your test.
Basicaly have patience, learn properly and safely and you will be a better driver for the rest of your life.
Good luck