How can I academically reform myself?

I'm a 16 year old sophmore, rising junior. I noticed that ever since 7th grade my grades have dipped downward, and its gone from 90's to mid-high 60's and low 70's and I have come to the harsh realization that if I do not fix myself now, I will regret my mistakes in the future. I go to school in a neighborhood where I have to concentrate not just on my academic life, but literally on staying safe, and preserving what little work ethic I have left. I've also began to play games more, though I am still very proactive about my future. If anyone can provide advice on how I can revert back to my previous academic performance, and...hehe get a little better at math while im at it