you need to do speed training. For ex. on a track run some real fast 400's and recover. Do that a few times concentrating on the time of each 400. Also interval training with sprint work. Gotta get those fast twitch muscles firing. PLyometrics 1-2 times a week help build those muscles. anymore than that and it might be too much. When running outside sprint (all out) every 2 telephone poles and recover every three, that will also help with speed. Proper stretching of the hamstrings will give you a bigger stride and enable the muscles to fire better as well. The more flexible a runner is the less restricted the running is. Happy trails!