When it comes to running long distance races, one of the biggest rookie mistakes is going out too fast in the beginning of the race. The best way to avoid the temptation of going out too fast is deliberately run your first mile slower than you plan to run the final one. It's tough to do, since you'll most likely feel really strong in the beginning. But keep in mind that for every second you go out too fast in the first half of your race, you'll lose double that amount of time in the second half of your race.