How do you train for a half marathon?
To train for a half marathon, build up your running volume over the course of a months. At first, start with just a couple of 2-3 mile runs per week. Then increase mileage no more than 10% per week up to 15-20 miles total per week. 

To reduce injury risk, do 80% of your running at slow pace. This will allow you to build an aerobic base without putting too much load on your body. On the remaining 20%, go hard and push your limits.

On the race day, make sure to get enough rest and eat a good breakfast. Try to do a warm up mile before the race even starts. Then during the race, find the pacer that is running at your speed, and stick with the group for most of the race. In the last half mile, sprint to the finish!