Everything mentioned above is pretty much spot on. I stopped going to meetings when I was 14 and was never baptized. I simply told my parents I wasnt interested in the religion anymore and I would no longer attend anything remotely related to it. Fundamenlist JW that my mother is, she wasreally upset but I didn't care. Leaving the org did not mean I wanted nothing to do with my parents so I was still respectful, responsible and did everything that was expected of me outside of the Org.
It's of vital importance that you continue to be a good daughter, this way they won't get the impression you want out of the religion in order to be rebellious, but just that you have your resptive disagreements and would rather not be part of it, therefore there is no need to fade - simply quit. But if your parents threaten to throw you out if you leave the religion I recommend you talk to your school guidance councellor. Also get an after school/weekend job so you can start saving money now! That was what I did and it helped tremendously when I left home at 17 yrs old.
Try to build up as big a network possible of friends outside the Org as mentioned before, this is extremely important. If I had not had a lot of friends when I left at a young age I have no doubt I would have found myself in dire straights.
You are at a huge advantage over most on this forum. You will be leaving before your life becomes too entangled and dependent on the Org, not to mention the indoctrination you've undergone is not as ingrained in you as it is for those leaving much later in life, you'll find your transition to living a "worldly" life to be pretty smooth.
Anyway, welcome to the place where we are all working on an anti-Governing Body vaccine! You're amongst an excellent community whom are genuinely compassionate. Any help you need or questions you have, please feel free to ask. We're all eager to help!