Select a reference image, or position a mirror near your workstation to view yourself in.
Create the basic shape of your head using characters.
Add hair to the head shape when you are satisfied with the shape. With hair and an outline, you have the basic framework for your portrait to build upon with detail.
Create features until the image begins to resemble you.
Change the font used to alter the shaping of the letters. With the many fonts that come default on all computers, you will have no shortage of potential shapes, even when you're only using characters.
Use varying font sizes to alter the appearance of your characters used. For example, an "o" written with a small font, with a period from a large font size in the center, makes an effective iris and pupil for an eye.
Skew and rotate the characters entered, if needed, to create the required shapes. Any manipulation of characters other than cutting off sections or splitting a character into pieces is permitted.