Running downhill is a great opportunity to take a little bit of a break from your run. But you don't want go too overboard and completely fall forward. There are a couple things that you want to be aware of when you're running downhill. When you're going downhill, you don't want to lean too far forward, but you also don't want to lean too far backwards, because that's just going to slow you down. So try to have that lean. Let the gravity help you go down the hill a little bit.
Watch where your foot is landing. You don't want your foot to land too far forward in front of you. Try to let your foot land right underneath your body. If you're letting your heel land too far ahead of you, that can send too much shock up through your knees and through your hips. So let your body lean a little far forward. Relax your shoulders. Use your arms to balance you. You don't want to go too fast down the hill, because it can actually cause a lot of stress on your quads. So let your body fall forward, but in a relaxed, controlled manner. Let gravity pull you down at a steady, controlled pace.