How can I become a faster sprinter?

I run the 400 meter and the 200 meter dashes. Times of 50.3 and 22.7. I'm not satisfied with these times. I graduated and I want to train over the summer so I can destroy these PRs and run 48 and at least 22 low for the 200m. Any tips at all that will help me get faster?How can I become a faster sprinter?
I also run the 400 and 200. Doing fly-in workouts really help improve your speed. Go to the track and start half way at the curve jogging and slowly build up your speed. Once you hit the 100 mark you should be at full speed and sprint all out for 40-50 meters. It really improves your acceleration. Also do a lot of bounding. Don't forget these races also take endurance so your gunna have to bust your *** with hard workouts. Goodluck!