If you want to improve 40, odds are that you're going to need to improve mechanics more than strength. This is hard to do without going to a trainer who knows what to look for.
However, some of the basics are pretty simple for acceleration: get your knees high (thigh parallel to ground), lean (~45 degrees) and make contact with the ground behind your hips
Here's some decent technique info:
How To Improve Your Sprinting Technique