Make sure to work on your sprints outside of practice as well as building up your core muscles. Core muscles help use your body to its full ability. Another good tip would be to work on more weight training for your quads, hamstrings, and calves. A place on YouTube that I've found some good workouts is to search for 1823rugbysevens. They have some exercises that would be beneficial. Besides sprinting, core work, and lower body weight training. Work on your flexibility. Whether its on your off day or free time your have after a workout, commit time to stretching, your muscles will be able to perform much better when there stretched and relaxed. Best of luck.
Google speed training, you can look at some youtube videos or some sites
