If you need to draw a demon monster in a hurry then watch this video to see how you can sketch one up in a flash. The great thing about sketching is that you can just sort of etch out the form, refining it until you have the scary demon you are looking for.
When starting to draw your monsters and demons, you can do a little exercise called drafting. This is simply a process where you begin to sketch loosely without having a clear idea what you are drawing in the first place. This may sound kind of vague, but it produces some good results. Try it out!
Once you have formed some ideas and rough sketches, you can then proceed to lay out your art in your own style and exactly how you want it.
Start to draw the rough shape of the head like in diagram 1.