STEP 1. draw the out line of the skull like in the picture, this dose not have to be perfect, the end step you go over it!
STEP 2. this step color the skull in, it dose not have to be 2 colors it can be any its up to you remeber to highlight the teeth dont have to but it gives it a 3D look!
STEP 3. last step, draw the eyes,nose,cracks and lines near the teeth, if you want to make it look 3D i highlighted one of the outer eye rings dark and the other light, really its up to you! remeber to outline the skull like i said in the 1st step it makes it look bolder! then your done!