In reply to JMGLondon: great advice there.
I ran my first half marathon last September, so might be well placed to answer. I got really into it and was running up to 50k a week in the peak weeks about 6-8 weeks beforehand. I had a background of running 2x a week of 6-8k each for a couple of years, on and off, beforehand. But since completing the Sydney half I have been unable to run due to plantar fasciitis, in spite of a fair bit of physio.
My two biggest mistakes were:
(1) stepping up my long run distance way too fast. Just because you CAN, doesn't mean you should. I did an 18k the week after a 12k, basically cos I felt fine and was lazy about planning the route ( it ended up a bit long and I didn't want to walk home). My ankle niggles started the next long run, and I think led to my current long term injury. The message here is that there is a lot of connective tissue in your legs that takes a battering, and it can turn into an overuse injury without much warning. Next time I might consider long runs on alternate weekends, and do moderate length Saturday *and* Sunday runs on the other weekends.
(2) just running. I put all my time and energy for sport into the run sessions, up to 5 a week. Pilates or yoga once a week, or a couple of half hour lower body strengthening sessions, might have left me uninjured. If I'd run 2h and been uninjured it would have been a better outcome. The time means nothing, esp if you haven't done a half before.
One good thing was doing a 10k a good while beforehand - useful to get accustomed to running and esp pacing yourself with all the other runners around. It's useful to do some tempo running mainly to get used to practising keeping the effort constant and stay at a given pace; also I found it helpful to do 2x3k at target race pace around 10 days before the run, to get used to that exact pace (and to decide if it is the right pace).
I reckon keeping it simple and focussing on run time, and gradually increasing time per week, while running varied terrain (rolling hills as well as flat runs), and doing some supplementary lower body strengthening, would be a good way to go.
Enjoy it and good luck, Andy