Block Work. Block Work is Essential to the 100m dash. I kno because I run it in College. My block work was horrible, I had always been fast but played "catch-up" the last 50m of the race. Work on that for sure. Also, do some speed workouts, jumpstrech, stairs. If you really want to do good work on some explosion workout out of the blocks and run for about 40m. Your not gonna get fast overnight, but running the stairs, and doing jumpstretch improves your speed. Do some 20m drills like HighStep Walking, Jogging, Skipping, Hopping.
When you do sprint workouts run 100% for a few reps at a short distance, than increase the meters and lessen the reps. I suggest start at 7 reps and work your way down. Make it a workout, 5 min break, 3 mins, whatever you can handle.