Obviously, you have to run a lot. Make your runs consistent in increasing mileage each week, but not more than a 10 percent increase any week. Right before the marathon, I aim to be running around 50 miles or so a week.
Add speed work and interval training to your runs, and have one long run planned every week or every other week. For the long run, go more slowly than usual, and have water handy.
Listen to your body, and give yourself time to recover, especially after the long runs.
Don't make radical changes to your running routine for the race. Make sure your running shoes are well broken-in, and don't add a water-belt, or GPS watch, or new running shirt, or anything at all that you haven't gotten used to in your training.