How do I get good grades in school?

I am a sopre in high school, and I am considered to be very intelligent, as reflected by my scores on the PLAN test and PSAT. I would like some advice on how to better apply myself in school so that I may improve my rank from 2 to 1. I am separated from 1st by hundreths of a grade point. Is it possible for me to attain first, and what advice do you have?