Check out these steps below, try it and use them to work more on your pace and learn how your body reacts to different paces and speeds. Once you get a feeling for that, use it on your next long run, you will experience "the runner's high" once you are comfortable changing paces and challenging your body.
1. Start out slow. It is very common for people to feel fatigue within the first minute of running. To make it over this initial hump or avoid it altogether you should set your initial pace extremely slow taking small steps.
2. Pick up the pace, drastically for just a few minutes. This lets your body know that there is work to be done. Your body will respond by doing all sorts of neat biological responses that are way beyond the scope of this wiki but ultimately will lead to your high.
3. Slow your pace as soon as you start to feel fatigue. This will help you regain your breath and your legs but your body will keep on doing those biological things. Plan on keeping your slow pace for 20-30 more minutes.
4. Let your speed find you. At some point in your slow run you will likely experience a sudden increase in energy. When you get this feeling you should be ready to channel it into a hard run. This is the zone where you will find your high.
5. Now start to run and see how your body responds. Once you start to feel winded you must push your body just a little further to find your high.
6. Once the runner's high hits you just go with it. The harder you run the better you will feel. After a few minutes the high will peak and then gradually fade. Slow your pace as the high fades over the next 5-10 minutes.
7. Finish out your run at a sustainable pace.