1. First and perhaps most important, you have to get plenty of fluid before and during the race. Try to drink eight to 12 10-ounce glasses of water or electrolyte replacement drinks each day leading up to the race. During the marathon, the standard rule is to take in 8 to 12 ounces of fluid every 15 to 20 minutes.
2. During a marathon, you need energy, too. If your stomach can tolerate banana slices, orange sections, energy bars or energy gels on the run, they'll bolster your blood sugar level. Sports drinks are excellent for this, too. Keep in mind that even the most highly trained athletes hit the wall when they've exhausted their carbohydrate stores, so be diligent about refueling.
3. You should do several long training runs at around 20 seconds per mile slower than your goal race pace. Two-hour runs at this pace develop the muscles' capacity to burn carbohydrate and fat efficiently. These runs also will prepare you psychologically, as you'll be running for a long time (as you will on race day).
I have my athletes complete four to six of these carefully paced runs on a hilly course during marathon buildup. We do the workout every two weeks.
Runners monitor their mile splits, take in water or an electrolyte drink at appropriate intervals and maintain a smooth, controlled effort. Some athletes experiment with different eating and drinking regimens during these runs.
You might also consider mixing in some long races (10K and over) at your marathon goal pace. These help the body to adapt to this particular pace.