Before you listen to me, please listen to your body. Don’t suddenly do some drastic routine or start training like Ivan Drago in Rocky. Training will take time and a lot of your patience. If you are serious about any form of exercise the interwebs are a marvelous place to Google training plans specific to your needs.
My nugget of advice for those thinking about half marathons is to increase your mileage gradually. When you start running you can get cocky, and you will end up pushing yourself because you feel OK during the run. It’s after a run that you realize the damage you’ve done. With this, I give you the 10% Rule.
How to Use the 10 Percent Rule
From About.com: Increasing the intensity, time or type of activity too quickly is one common reason for sport injury. To prevent this, many fitness experts recommend that both novice and expert athletes follow the ten percent rule, which sets a limit on increases in weekly training. This guideline simply states that you should increase your activity no more than 10 percent per week. That includes distance, intensity, weight lifted and time of exercise. For example, if you are running 20 miles per week and want to increase, adding 2 miles the next week follows the 10 Percent Rule. If you are lifting 50 pounds and want to increase, add 5 pounds the next week to follow the 10 Percent Rule.
Another sweet trick is to start running for time, not mileage. You should know your pace and be able to gauge how many miles you can conquer in a given amount of time. I would set mini-goals for myself, say hitting 45 min on the weekend, this way I could focus on staying calm and paced throughout the run instead of fretting that I was running a really slow mile.
In a nutshell: apply the 10% rule and watch the clock not the mileage.