2009. A year for a change. 15 year old in need of advice please.?

Hello. I am a fifteen year old girl and I am going to start a new school term in my first year of high school, in January. I have not been the most focused and brightest last term but that was last year and this is 2009 and I am determined to become different. I am doing my GCSES next year and I am aiming for all A's, a couple of A*'s if I am lucky and the minimum I will allow myself to get is a B in science and maths. How can I become an over achiever and stay determined without turning into a self confessed geek? Also how can I get a part time job, there is nobody hiring? Also what sort of things could I do to enhance my chances of getting the jobs I want to be? An actress/broadcast journalist but perhaps studying in university to become a solicitor or a psychologist as a backup plan?