Three things:
1)
Posterior chain strength. You really need to increase the strength of your posterior chain (calves, hamstrings, lower back, traps) in order to run fast. Start doing deadlifts, preferably with a snatch grip, right now. Adding a few speed-strength moves like power cleans and
power snatches is also a good idea.
2) Stretch like there's no tomorrow. Stride length is a huge part of running speed. If you have a truncated ROM due to not stretching properly, you will be slower. Make sure to thoroughly stretch after each and every training session. Focus on hamstrings, hip flexors, adductors and glutes.
3) Practice. This might sound stupid but the best way to run a faster 40 is to improve your starting position. The less time you spend in the blocks the faster you get to the finish line. Getting the right starting position can shave up to 3/10ths of a second on your time. So get someone, an experienced track coach, to show you the proper starting mechanics and practice them a lot.