How Can I increase my Speed and Agility?

First off, I am training for football. That being said….
I was wondering what are some ways to get faster? I can run a 40 yard dash in about 5.2 seconds… and compared to other people, that’s slow. What are some ways that I can improve upon my time? My starts are dead on, but I’m not explosive out of the gates so to speak.

I want to be able to run a 4.3 if possible. Any Ideas?