How should I lift weights?

Hi, I'm 14, and I have only lifted weights a couple of times. I dont really know if i'm bench pressing right, but I think I am. I am strong, but I can't lift that much. It's weird. I do 2 sets of 10 then 1 set of 5, probably with 70 lbs, what do you suggest me doing for reps? What else should I do besides bench pressing?