Drawing dragons is a particularly difficult subject, mostly due to the fact that they are extremely rare or otherwise (most people think anyway) mythological. But with the correct guidance it can be done.
As a sort of introductory lesson I will teach the head of the dragon from the side view. Then get on to the full body, and individual body parts in future lessons.
Step 1: The Actual Base
Although probably the easiest, this step is essential to the process of drawing not just the head of the dragon but the body as well. Additionally, determining the position of the the head relies on this very step.
To execute simply draw a circle or sphere, then continue with the jaws from the circle.
Step 2: The Upper Jaw and Brow
From this step forward the actual design of the dragon is completely up to you, but I have drawn an example for you to start off with.
Remember not to press so hard with your pencil for these 'base steps'.
You should also take into consideration that the brow is quite significantly higher than the nose/snout, so when drawing the top, slant it down a bit.
Begin at the top of the head continuing down to the tip of the snout. Now while drawing the mouth line make sure to draw it ridged and pointy, with lots of dips and erections. Continue the mouth all the way down to the jawline, which is perpendicular to the eye.
Step 3: The Lower Jaw and Jawline
In my opinion, the jawline is like the glue that holds the whole head together. Its what makes a dragon fierce and vicious, it determines where the eye goes, its where the mouth line stops, and its at the center of the face. Drawing the jawline is essential to making a good dragon and should NOT be forgotten.
The lower jaw continues from the jawline and is significantly thinner than the upper jaw. Also, the lower mouth line is more straight than the upper mouth line.
At this point you can erase the guidelines you drew in the first step because there is no longer a use for them.
Step 4: Details Such As the Eyes
Now we are headed into the details of the dragon head. The eyes are perpendicular to the jawline. And should not go past the brow line.
Dragon eyes are like a combination of human eyes and feline eyes. They have the shape of human eyes, and have the pupils of felines.You should also keep in mind that you shouldn't draw them too big, lest they'll look cartoony.
There are also the holes in the skull which can be seen through the layer of skin as indentations. These holes apear below the eyes, in the middle of the upper jaw and a small one in the middle of the lower jaw. To draw these indentations you need to determine your light source. Mine was above the dragon, so naturally the shadow was cast on the upper side of the indentation. But do what you want.
There is also that little bit of webbing in between the jaws that give it that extra bit of realism. Like the eyes though, don't draw it to large.
Step 5: The Teeth, Horns and Tongue
The teeth are quite difficult because there are so many different kinds of them. I like to stick to the variation where there is no gums, but don't let me stop you! After all, they are 'mythical' aren't they?
The horns are easy, simply pick a shape and draw it!
The tongue is usually 'wavy' and quite thick. Avoid forked tongues, unless you want to draw an eastern dragon (Coming soon!).
Step 6: Final Shading and Details
From this point on I'm going to assume that you know about shading, shadows, highlights, etc. If you don't know how to shade, just find another instructable (I might even make one).
Start by shading those indents we talked about in step four. Then continue to shade the horns and tongue. You should also shade that webbing in between the jaws making very distinct contrasts between light and dark (this creates a glossy, wet look). With a sharp pencil detail the eye muscles. And finally, draw a few scales to define the texture of the skin.