You need to spend time on sprint technique first. Mark off 10 and 20 yards and do two of each of the following drills at 10yds and two of each at 20yds
-high knees; concentrate on getting your knees as high as possible and get as many strides in as possible. Don’t worry about your arms or the speed at all.
-toe taps; same as above, but with regular knee height, as many as possible (it should take a long time to cover 10 or 20 yds)
-heels to ass; same concept as above, but make your heels hit your ass on each stride
-exaggerated stride lengths; start a few yards behind your normal starting point and sprint at 75% speed. When you hit the starting point, use the longest strides you can
-arm swings; as many strides as possible (like the toe taps) and swing your arms as quickly as possible. Your arms should stay bent at 90degrees throughout and use your shoulders to swing
-find a moderately-sloped hill and run down it at full speed. When you level out at the bottom, maintain the same lengthened stride that you have to use when coming downhill. This will improve stride length.
the whole time you do this, make sure your head is very slightly in front of your hips and your feet land directly below your head. During normal sprinting, the balls of your feet should hit first and hit directly under your head. The heels hitting first creates a slight braking action. During the start, lean forward, keep your head down and your arms swinging high for the first 2-3 strides.
By the tenth step or so, you should be fully upright. Do not lean forward-this will make your stride length shorter and make it harder to land on your toes right under your head. Work on your starts by running 10-20 yd sprints at 100% or with a chute or sled and work on your stride by concentrating on the above drills’ concepts (especially stride length) while your run sprints out to about 80-100 yds at 70-90%.
Once you improve upon technique, pick a distance that you want to be really fast at, and run a lot of sprints at 20-60 yds past that along with working on your starts. If you want to run the 40 well, work on 10yd starts and run 60’s 80’s and 100’s. Run the 40 just to incorporate all of the techniques together. You’ll also need to do a little bit of long-distance to keep your endurance up. If you’re gassed after a few sprints, you won’t be able to run enough to make serious progress. Run a few 200 yd sprints along with 1-3 miles about once a week, maybe every 10 days.
You can do the drills everyday, but the sprinting itself is up to you. Whenever you’re sore or plan on lifting legs that day, just do the drills. Stride length is the key to the technique part, so stretch the shit out of your hamstrings and always try to stride as long as possible, even at the start. This info should give you a pretty good foundation to build on.