Remember the saying that practice makes perfection, it's absolutely true when it comes to being able to improve on your speed. There is no way of getting to increase your speed without getting a lot of speeding enhancing drills that would help sharpen your agility, acceleration and fitness. If you have low fitness, low agility and low acceleration, there is no way of getting to have an increased speed when you are running because you are most likely going to pass or gas out within the shortest possible time.
There are so many drills which you can take-up in order to increase your speed, some of them are practicing shuttle runs, long run, mountain climb exercises, lunge exercises, swimming, cone running drills and croaching with ladder drills.