1) To start off, you'll need a picture of someone. Make sure the photo has some good lighting.
2) Think of a color that would be great with the photo. In the end, I chose pink to be the color of all the shapes. I used different shades of pink to make it.
3) Open Adobe Illustrator along with the photo and select the pen tool.
4) Notice I have pink as the color since I am going to use this as the primary color for the shapes. Make sure the settings are the same using this as a reference.
5) Start by making small polygons and creating more beside it. Notice how I applied different shades of the same color to each polygon so your could tell there difference between each one.
6) You can see that I adjusted the colors so they weren't too dark or too light. Just keep doing this until your done with the face.
7) To make the hair, I used one solid shape and added small lines the symbolize the strands of hair. You can design the shapes of your vector illustration but use your imagination!
8) Create a simple background that matches with the shades of colors on the shapes.
Finished Product!
Here are some sample pictures for inspiration on your illustration!