moving up to half marathon question/advice

I'm sure you'll get more detailed suggestions, but if you've had injury trouble in the past and didn't race longer than 5K, yes, just start by increasing your mileage with easy miles. As you get accustomed to higher mileage, do strides after easy runs a few times a week. Then start doing tempo runs, maybe cutting back the distance a bit to make sure your legs can handle the extra intensity. For a half, I think tempo miles are more important than speedwork, especially if you've had injury trouble. Once your legs are accustomed to tempo pace, you may want to try some long hills instead of track VO2max intervals. Assuming you're in the northern hemisphere, it might be best to plan on a fall half, with a 5K & a 5M or 10K in the summer or early fall to get you used to racing again. Good luck.

This is perfect advice. Don't feel the need to add in workouts until you get your mileage to a good place. Spend a month or two building your base. Idk what a reasonable target for you would be but maybe something like 50-60 miles. You could do that on 6 or 7 runs/week. Basically 3-4 days of 6-7 miles. 2 of 8-10+. 1 of 12-13+. Do strides twice/week. Don't think twice about your easy pace. Easy days should be easy. When you are ready for workouts, don't worry too much about the VO2 max stuff. If you were doing a 12 week build for a half, you would only do a handful of those workouts & they wouldn't come in back to back weeks. Start up with tempos & threshold repeats with good volume. Instead of doing a 20:00 tempo, try to go a little longer. Break it up if you need to with short jogs to get in better volume -- 12:00/10:00/8:00 @ T or 3-4 x 10:00 is more time at pace than 20:00 straight. You're probably used to doing 5 x 1k @ 5k pace. For half marathon training you'll want to do ~12 x 1k @ T off of short rest.

I totally agree with the other posters. And I just wanted to toss one other thing out there in case you wanted a more specifically written out plan. In his book Faster Road Racing, Pfitzinger has some very nice base building plans. They have you stair step your mileage up nicely, gradually introduce strides and then manageable tempos. He's got 10 week programs to help you build to either 30, 45, or 60 miles a week. So you can pick what feels best to you. Or just look at them (the book is available at most libraries) and use them as a guide.

Why?

Good advice.