Hi all, Lots of good advice on here already but just thought would chip in as well. Ran my first marathon in Paris a few weeks back, chip time of 3.29.36.
It does seem to be a running truism that for any rule or advice, however sensible, there's always exceptions - people who do it off the back of two runs a week, or on nothing but water, or always at the same pace. But, for what it's worth, my advice would be:
Be flexible with your schedule. It's worth taking the time to put together a really good schedule, but you need to make sure it's realistic, there's no point committing to runs that you know you won't make, and you need to be prepared to accept that sometimes the best thing to do is rest yourself for the next run.
Nutrition, again one of those 'each to their own' areas, but I found Lucozade Sport and the Lucozade gels good. Would also eat bananas on long runs, and occasionally sandwiches. Take the gels with water though or you might feel sick. Make sure you drink something (pref isotonic) as soon as you get back and if it was a hard session maybe some eggs on toast to help repair your muscles. Also eat a good diet generally, and you can get away with the odd drink unless you're trying to keep your weight down.
Train well, but don't forget good quality rest. When you train, you overload and damage the muscles, and it's in the rest after a session that the damage repairs, and the muscles are stronger. I'd also suggest to vary your pace in training. Pace on LSRs can, I feel, be as slow as you like, but I also do a speed or hills (or fartlek) session on Tuesdays, and a brisk mid-long run on Thursdays, at faster than marathon pace (maybe 7.45 per mile), building these from 7/8 miles up to about 15.
Hope that helps!!