Good way 2 study for Midterms?

My midterms are in one week, and I want to know the best way to study for them.

I'm in 9th grade, and I have been a good student, but I've been slacking a little and wasting time on the computer. My averages were ranging from 94-97, but now are down to 90s. I need to do really well on my midterms because they count as 1/6 of my final average. A good grade is crucial for me to stay on the Dean's List at my school.

p.s. I'm nervous because I got an 88 on my math test & it was the last test for the quarter. :c

Thanks for all your help! :)