If you are brand new to the sport or if you are starting up again after a long break, I suggest you consider the following.

1. Run for time, not distance.

Don't worry about how far you run. Try to get in twenty minutes of exercise with each outing.

2. Walk

Rather than trying to run for a full twenty minutes, set smaller goals. Run for two minutes then walk for two minutes. Repeat this cycle for the full twenty minute workout.

3. Increase slowly

It is better to proceed a little slower and avoid injury than earn bragging rights about how far/fast you can run immediately prior to a hamstring pull.

If you are doing a run/walk combination, do not increase the length of the run any more frequently than once per week.

If you are running increase distance/time no more than 10% per week.

4. Enjoy

Stay at a pace you can be comfortable with. Your speed and endurance will improve with time. Make sure you are not exhausting yourself. Enjoy the run.