How to get straight As in 11th grade ?

I'm 16, in 11th grade, and as you all know 11th is an important year for my future, more important than 12th grade actually. Anyway I am trying really hard to get 90% and higher in every cl, but I haven't been. I would like ways to study and work etc. so that it is almost guarenteed, with hardwork and dedication from my part of course, to get 90% and higher thank you !