Andy's just secured a place on the Great North Run (fantastic!) and asked me (of all people) for a few tips based on my Marathon experience. I did a bit of a brain dump and this is what I came up with (disclaimer: I'm not a professional athlete not trainer nor physiotherapist. I'm not even very good. But I did learn a few things along the way to at least completing the London Marathon)

1. We used the Nike training schedules at http://www.nike.com/europerunning/?ref=http://www.nike.com&l=en_EU#train|train_tool -> Training Schedules. There’s a beginners 5km schedule if you’ve not been running and you can build up from there. For longer runs you usually get some training plans from the organisers as well but they should dovetail nicely and the Nike stuff allows you to get a bit ahead of the game.
2. You do need to plan your life around training to an extent – particularly in the latter stages when you’re doing longer runs. You’ll probably be running 3-4 times a week and for some reasonable distances. And it’ll take it out of you – particularly the longer runs at weekends so just be aware and try to plan things in advance.
3. Don’t beat yourself up if you miss a run but by the same token try not to miss too many.
4. Do whatever you can to avoid injury. As the distances increase your chances of injury increase. I found that up to about around the 2 hours ish / half marathon distance was okay but distances beyond that tended to make bits of me ache in a way that clearly wasn’t normal.
5. Injury is a double whammy because [a] you’ll worry you might do it again / aggravate it when you do return and [b] you lose a lot of training runs in the interim. Make sure you warm up and, in my case, I pay particular attention to my Achilles as I injured that in my marathon training and it’s still not right.
6. Try and find a training partner. It’s a lot more fun with a partner and it’s also a lot more difficult to miss a run.
7. If you can, try and find somewhere pleasant to run (especially at the weekends when you have a bit more time and longer runs). It’s amazing how much more enthused you’ll be about a run around (in my case) Windsor Great Park than around the block – it makes a big difference motivation-wise.
8. Running in daylight is much more pleasant than running in the dark. This’ll be less of an issue for you are you’re training through spring / summer but for the Marathon it’s mainly winter so it’s difficult to avoid the dark. And running in the dark increases your risk of injury.
9. Make sure you have decent running shoes. Go to a running specialist shop and have a chat to them. They’ll assess you and advise on appropriate shoes. They don’t have to cost the earth - I think my marathon pair were about £50 which I thought was very reasonable.
10. The drinks bottles with a hole in the middle (ie it’s quite slim so easy to grab) are great. Get the 500ml one and you’ll be sorted for all but the longest runs. For those long runs you’ll probably want to plan a route that consists of 2 loops so you can leave drinks somewhere along the way. That way you don’t have to carry all your liquids with you all the way around.
11. There are some very good sites for mapping your routes (and getting accurate distances) eg http://www.mapmyrun.com or http://www.walkjogrun.co.uk.
12. Running on a treadmill is okay if you need to but running outside is harder work (both physically draining and also on the joints). So by all means do some training on a treadmill but I’d recommend doing most of your training outside if possible.
13. I put this here just so there weren’t 13 points.
14. Enjoy yourself. Find a nice place to run, ideally away from traffic and with nice, flat, metalled roads / paths or firm grass and have fun.

I'm sure there are lots of folks out there who are fitter / faster / more experienced than me so feel free to leave a comment if you have any other advice...