How do you train for a marathon?

I signed up to train with a local running group. We followed Jeff Galloway's method, which is a progressive mileage method that takes several months. When I started, I could barely run 3 miles. By the end, I was able to successfully complete a marathon! It was a great experience. Google Jeff Galloway's web site and you can get details AND links to local running groups that follow his method. Good luck.

run your *** off

you start running progressivly longer distances starting 6 months before the marathon and starting at one mile. about one month from the marathon you should be able to run the full distance

As most have already said you will have to progressivly increase your milage....now i'm not sure how much you run a day now, so i can't tell you when to start your training. but you should be able to run 13.5 easily at one time before you enter....i would personally make sure that i was up to running about 15 miles at one time a day at a hard pace, that way ur 13.5 will seem much faster and easier....as for the warm up....i would stretch then run about two or three miles with about 15 min left before the race and start stretching again to make sure that you are all loosened up. just make sure that ur heart is beating pretty good and your breathing kinda hard after your warm up and youll know that ur warmed up.