Your aim: You run at least once a week for an hour or more, and you want to improve on that, get fitter and maybe even train for a half-marathon or a marathon. Why not?
If you want to improve, you need to work on your stamina (so that you can run for longer) and your fitness (so that you can run faster). It's tough on your body, so you need to up the ante gradually to avoid getting exhausted or injured.
Your program: You need to do 3 runs a week if you want to achieve your goals, with 1 recovery day minimum in between each run.
> Your first and last run of the week should involve interval training (speeding up for a defined length of time and recovering at your normal pace). Interval training is used by professional athletes. It improves your body's resistance and ups the level at which your body releases lactic acid.
> On your second run of the week, go for a normal endurance session without pushing yourself too hard (around 10 miles at a heart rate of 140-150 beats a minute). This will help your body recover from your other sessions, improve your endurance and your body's ability to use oxygen more effectively.
> As you build up your resistance you can push yourself further and further each week, running faster for longer without tiring yourself out.