Learning good form will definitely help you become more efficient, which allows you to run faster and longer by expending less energy. This idea can be taken further by thinking of ultrarunning as an exercise in efficiency. Your goal should be to expend as little energy as possible throughout the entire race.
When I race, I try to eliminate as many wasted movements as I can. I only lift my feet high enough to clear the highest obstacle on the trail. When running up and down hills, I try to relax my muscles as much as possible and take short, easy steps. I limit my arm swing to the absolute minimum. Every wasted movement burns more precious calories.
You can incorporate efficiency by actively focusing on running as smoothly as possible. Good form, as discussed earlier, will create a noticeable difference in energy expenditure. Always look for other ways to reduce movement. For example, I tie my shoes in double knots so I won't have to re-tie them during the race. It's a tiny detail, but many of those little details can add up.