Nutrition
Months before your race, figure out what food you're going to eat in the race. Everyone's body reacts different to different foods, especially in long races. It's good to know ahead time what foods help keep you going and what foods hold you back.
Test Everything
Similar like nutrition, you should test everything else. Clothing, shoes, gear, hydration. You should plan out everything you're going to use in the race. So that way there aren't any unexpected surprises like chaffing or foot problems.
Make Your Workouts Harder than the Race
To help make race a day a little easier, aim to make your workouts harder than race day. You'll thank yourself later now.
Be prepared for the Death March
When you go beyond 5 or 6 hours, you might start to hit a wall. Which many people call the death march, mental prepare yourself for this part of the race. And know it's very likely there will come a point in the race when where you feel terrible.
Practice Staying in the Moment
Thinking about what's left when you're half way through, can make you feel like it's impossible. So stay in the moment, focus on what's currently in front of you.
Expect the Unexpected
Know that at some point something unexpected things are going to happen. The best way to handle this is to have a plan in place for how to handle it.
Be Positive and Have Patience
One of the most importance things you can do is mental train yourself to be positive and have patience. Good things take time.