Either work from a mirror or a photograph for this project and use a good painting program such as Photoshop. It's best to use a graphics tablet, but can use a mouse. Start by blocking in the main shapes using 3 or 4 colours.
Using a mid-shade skin tone colour, outline the features on the face.
Working with one shade darker, add more detail to the painting. Using one shade lighter, smooth in the skin tone by using a low opacity brush and the smudge tool. Add a little bit of detail to the hair.
Add all the main highlights and shadows to the skin tones, making sure to smooth in the colours as you go. Use a thin brush and darker tone to add the details, such as the mouth and pupils of the eyes.
It's time to get colourful. Use a low opacity brush to add colour to the eyes, lips and cheeks.
Use a thin brush and scribble detail in to the hair. Use the burn and dodge tools to add further, more subtle, highlights and shadows to all areas of the portrait. Continually refine all areas of the portrait by smudging or re-painting where necessary.
In the same way, take a thin brush and a light hair colour and scribble in detail where the hair highlights. Add further shadows and saturation to the lips.
Use the push and dodge tools to add further, more subtle, shadows and highlights to the hair. Using a low opacity soft brush, add small amounts of colour around the eyelids.
Finish up all the areas of the portrait and then add a nice background.