Knowing how to run the hills makes a huge difference in a race. To be a dominant cross-country runner, you need to master hills—not just climbing up but racing down as well. Running hills requires not only stamina, but also intelligence and skill. (It also takes some strength.)
During your preview of the course before the race, make mental notes about the hills, like their location and condition. Where are the steep sections, the flatter sections? Is the footing solid or loose? And are there any sharp  turns? Armed with this knowledge of the course, you can now focus on the skill of hill running.
Uphill Running

1. This is difficult, because you are essentially working against gravity. To do so effectively, you need to get both your mind and body right.
2. Anticipate the uphill. A few strides before the actual climb, try concentrate on your breathing by taking a few deeper breaths. As you blow tout, relax your cheeks and shoulders.
3. Stay strong and steady in your effort uphill, but don’t try to attack. The amount of energy you expend surging upwards doesn’t equal the distance traveled.
4. Stay tall and carry on. Keeping your torso up keeps your lungs large and allows you to breathe in more oxygen.
5. Run over the top. Because you have kept a strong and steady pace, with your torso up and lungs full of air, as you crest the hill and it gets less steep, you will naturally surge over the top.

Downhill Running

1. When you run downhill, the force of gravity pulls you forward, helping you run faster. You waste a lot of energy if you try to overcome this force; take advantage of it.
2. Use your arms for balance as you run downhill and your speed picks up. Your arms need to counteract your lower body. Let your elbows swing farther away from your body, and don’t be reluctant to put your hands up for balance.
3. Maintain a slight forward lean; don’t lean back against the hill. Take advantage of the incline by keeping your posture tall and leaning forward at the ankles. This will keep you balanced over your feet, maintaining a forefoot strike and keeping you nimble on the descent.
4. Land on your forefoot. The biggest mistake you can make running downhill is to continuously land on your heel. This slows you down by producing a tremendous amount of force on your body that zaps crucial energy reserves necessary for a strong finish. Instead, think about taking short, quick steps and increasing your stride rate. With the proper forward lean, your foot should land underneath your hips, not out in front. A proper foot strike might feel like a shortened stride, but in fact it is the best length for optimizing your momentum.