We're all different and can train at different levels. Here are my thoughts for your consideration (I'm assuming you're training for your first half)
1. Work up to 35-40 miles per week, doing one long run, one medium run, and the rest shorter rest runs.
2. Get your long run up to 15 miles and your medium run up to 10 miles. 5 or 6 miles is good for the rest runs.
3. Run your long runs for several months so your body gets used to that distance. By doing this, the half will be a piece of cake. Vary your long runs from 13 to 15 miles so you don't do the same thing every week.
4. In increasing your distance, follow the 10% rule such that you make small increases in distance every week or two. It's like climbing stairs, you can take them one at a time or two at a time. One at a time is less stressful on your body.
5. Run heavy stress/light stress by following your medium and long runs (heavy stress) with a light run (light stress) or cross training such as light swimming, light cycling, walking, or a day off. Your body needs at least 48 hours to recover from a heavy run. Running actually damages body cells. Your body repairs the damage and becomes stronger during the rest after a heavy run.
6. Don't mix increases in distance with speed training. Both distance and speed put stress on your body, and by mixing the two you can easily overdo your training.
7. Learn the symptoms of overtraining and when you have them, give yourself more rest for that week.
8. Let your first half be a fun experience. Setting PBs can come later.