Run everyday. Push yourself! Im the only girl that does military training at my highschool and you won't believe how much better I got at running from practicing everyday. Put effort into it. It's all mental. When you feel tired keep going! If you stop every time you get tired it will take longer for your running and stamina to improve overtime. When I would stop running my fellow cadets would yell and motivate me to keep going. We never leave a man behind so they would stay with me to the end. But I would force myself to run with them anyway, and it would hurt so bad i almost threw up several times. I came home every night exhausted but trust me it really pays off. I can run long distances and i feel so much healthier! Now I'm not saying you need to be all extreme and go all military style to improve, but just run everyday and push yourself to the maximum.
Maybe for the first few days you run to the end of your road. Then while still running to the end of your road you push yourself to run for a little longer, and a little longer each day. This is how i first got in shape. I can now run 5+ miles. It really works.