In a surprise victory, the forces of Athens routed the Persian forces of Darius I at the Battle of Marathon. The combination of exultant victory and fear of naval reprisal lead to one messenger, Pheidippides, being sent over the long mountain pass from Marathon to Athens. The bold messenger crossed the 26 miles with incredible speed, delivering word of victory, then promptly dying of exhaustion. Whether or not the story is true, it is the genesis of our modern marathon and the inspiration for thousands of runners who attempt one every year. Follow Pheidippides example, except for the dying part, by training for an attempt at a half marathon.
The goal of a half marathon is endurance, not intensity. As such your training should focus on putting down miles rather than speed. One of the ways to be certain you are training at a suitable pace is to run with a partner and talk for the entire run. Ideally, you'll be able to converse consistently throughout. If you are too out of breath to talk, slow down.
Most training guides for half marathons recommend you begin training three months in advance. Never leave yourself less than a month to train. Experienced runners, those who have completed 10k and 5k runs, may be ready in a month, but less experienced runners will need at least three. Keep your training schedule consistent and plan your schedule around training.
Ideally, you should be running three to four times a week. Typical schedules should involve three days of running shorter distances, followed by a day of rest and and a day of cross-training. On the sixth day, attempt a longer run, perhaps beginning at 4 miles and ramping it up by a mile or two every subsequent week. Take the seventh day to rest. At this pace you should be capable of running a 10-miler by the end of the third month.
If you need to rest, rest. Working at peak capacity is more important than running sluggishly over the entire week. Days scheduled for cross-training can easily become rest days if there is a need. Make sure to rest or cross-train, preferably something low impact like swimming, the day before any long run.
While you should stretch before every run, dedicating one day of the week to stretching or light-weight training can be an effective way to cool down and relieve some stress. Small weights with high repetitions are ideal for runners working toward all-body endurance.