The advantage of doing the Class 1 medical is that you can rule out any conditions that would prevent you from becoming a professional pilot.
However, the main conditions in young folk that stop are diabetes, dodgy eyes (ie strong-ish prescriptions) and colour blindness. If you don't know the status of these conditions, find out.
If there's a mag with a current article out, buy that. I believe Clive Hughes has written a pretty good book about it all too.
Google GAPAN and there should be some info about it all too.
Study hard at school, do some team sports and get a part time job to earn some cash.