Jelli, I started out following a Runners' World training plan, which I think was recommended on the other running thread (the one where they are all doing marathons/half marathons). I have it in PDF format, so if you want to PM me your email addy I can send it to you to look at?
But I should say that I only followed the first few weeks of the plan, which involved 4 runs a week and some fairly (for me) brutal mileages. I was finding it hard fitting everything in and my knees were hurting. And it was Christmas/New Year etc. I can't blame the weather this year as it hasn't been that cold.
Separately I read that a half marathon was a 10 mile run with a 5k added on the end, and that if you could run 9 or 10 miles, the adrenaline on the day would get you through the rest. So I worked up to 10 miles (with my trusty Garmin 
), which I've done 3 or 4 times now. I also did a 10K "race" last week (it was in the plan, which was why I signed up for it). I say "race" because I wasn't racing against anyone but myself.
The half marathon is 2 and a bit laps of the park, and there are a couple of really horrible hills. So yesterday, which will have been my last long run before the half, after I ran the first (worst) hill I cut back across and ran it again, so that I could tell myself next week that I'd run it twice in the same run and it wasn't going to scare me (IYSWIM). I also did a second lap of the bottom bit, as that's the bit I'll be doing three times. Because I run regularly in the Park I have plenty of landmarks, so I tell myself I only need to run to the next light/water fountain/hot dog stand/oddly shaped tree before I can slow down.
A friend of mine - who is very fit, also bikes and swims - recently did a half while recovering from an injury so ran 3 mins/walked 1 min throughout. I noticed people walking bits of the 10K last week so have decided that there is no shame in walking a bit if I need to. Yesterday, because I hadn't been out all week and didn't want to wreck my knees, at the end of each mile I walked for .10 of a mile. I ended up doing 10.8 miles in that fashion. I'd already walked 3 miles yesterday morning, so I now know my legs can do the distance.
The thing that will get me round on the day is that I'm doing it to raise money for charity and I don't want to let people down. DH is also doing the run, but will be faster than I am so has promised to be waiting at the finish for me, which if last week is anything to go by will be a nice boost at the end (assuming his legs are still working - he is aiming for less than 2 hours).
Sorry, that turned out to be a bit of an epic!