Get some caffeine in your system.
As for that cup of coffee with breakfast, go ahead and have one. "Caffeine boosts endurance performance by affecting brain chemistry in a way that lowers perceived exertion, or how hard it feels to run at a given pace," says Matt Fitzgerald, a running coach who is one of the coaches for one of the best marathon training aids, the PearSports run tracker. Fitzgerald suggests taking a caffeine pill instead of coffee an hour before the start. "But it only works in those who are not habituated to caffeine," he says. His advice: Go caffeine-free one week before the race to get the full effect.