Probably the only boxing advice I will ever feel comfortable giving. Been boxing for about 5 years. The one thing I can pass on to anyone starting out is how to avoid knee pain while throwing a straight right.
For several years I was obsessed with 'putting the cigarette out' twisting my right foot instead of turning my right hip. I would really exaggerated that motion and my right knee suffered. Past six months I've learned to turn my right hip over and have ignored the 'put the cigarette out' motion. Its there but the movement can't begin from the foot and go up, it needs to start at the hip and go down. No longer have knee pain and I hit harder. Pretty basic, but not the kind of advice I got for several years.