How can I become a really good fast bowler in cricket?

Look, I am an opening bowler, and let me tell you right off the bat, it is not easy. I have been playing in a league since '03. It is good you have line and length, but what you need to do is also build up stamina, a thing needed for pacers. Lose weight. Work out. And since you slow down approaching the crease, shorten you run up. And try bowling with a leather ball. Tennis won't get you anywhere! It is easy to get thrashed in them. They are ok to start with, but move to leather. Try aiming a a certain area on a wicket, and see how many times you can hit it while bowling. Try improving this every day, and you will get good line. To have a smooth action, shorten your run up and lose weight. when you release, release with your hand that has the ball in it almost touching the ear. Do this. I hope I helped!