Choose a photo of a human to use as a resource. Try to choose a photo that captures that individuals personality.
Also, decide on your medium. You may choose either vector drawing, pencil drawing or colored pencil drawing.
If using pencil, begin your sketch using correct proportions and observation make a line drawing of your person.
If creating a vector image transfer your image into Google Drawing and review tools in program.
Add a full range of value to your image. Be especially vigilant if you chose colored pencil...you will need 10 different values in the skin tone too!