First, draw a circle on the head where you'd like the eye to be. Be sure not to place it too low on the head, or dead center - you'll end up with a strange looking critter (unless, of course, that's what you want to get).
The cheek of a dragon is filled with muscle to clamp the jaw shut, so it's large and bulbous. The muscle here is located right below the eye, and is a large triangular area. Imagine ropes of muscle right below the eye all stretching down to connect with the base of the jaw... Next, you can throw some brows on to protect that eyeball. I usually have the dragon's horns extend from the brows. I envision brows as cylindrical tubes of bone extending from over the eye right up into the horns.
Finally, you can add the nostril. Again, this is like a bent cylinder shape, or a kidney bean shape, even.