I think its important to hone both stamina and speed. For stamina, your doing the right thing, which is practicing. Try longer distances such as 3/4 miles, so you will become more comfortable in the 2 mile run.
To build up speed, you need to increase the muscle mass in your legs - the 3 big muscle groups you need to target are your quadriceps, calves and hamstring. I suggest you do lunges, squats, jump squats, etc. If you have access to a gym then do leg presses, leg curls, leg extensions, squats with weights, dead lifts, calf raises.
Although I said to focus on your leg muscles, don't forget the rest of your body. Some power is generated in the upper body, especially when pumping the arms. Lastly, stretch before every workout and drink plenty.