Congratulations! Independent reading is one of the best things you can do to improve your academic performance and develop your vocabulary. When I answer questions like this, I always like to know what was the last thing that you read that you really liked. We can't do that so here's a few I recommend:
The Call of the Wild by Jack London--If you missed this during your piror education, it's worth reading. Use enotes to help you decipher the layers of meaning.
Feed by M.T. Anderson, a science fiction novel.
You Don't Know Me by David Klass
The Book Thief by Markus Zusak. It's based on the Holocaust, but the characters are amazing.
Soldier X by Don Wulffson about a German boy drafted into the war.
Looking for Alaska by John Green covers friendship and the fringe part of adolescent live.
Catcher in the Rye by J.D. Salinger is a must-read at some point, preferably several times at different ages.
Perks of being a Wallflower by Stephen Chbosky. It is a blend of Looking for Alaska and Catcher in the Rye.
The First Part Last by Angela Johnson
Under the Wolf, Under the Dog by Adam Rapp
Don't forget to check out graphic novels like Superman, Batman, V is for Vendetta, Full Metal Jacket, and Bleach.