First step:
Ask Permission!
I asked [link] if I could do a pixel doll of [link] She said yes, so I...

Second Step:
Thank them.
...thanked her and promised the base itself and a tutorial for her.

Third Step:
Place the desired picture in your work space.
Mine was MS Paint. ^^

Fourth Step:
Outline in an Easy-to-See color.
Since the picture was Black and white, I used red.
If picture has hair and clothes you wish to include, do each piece in a different color, so as not to get confused.
If you can use layers, I suggest you do so... If you do, skip the next step and simply delete the regular picture.

Fifth Step:
Delete/Erase any other color than that of your outlines.
Using MS Paint with this step was fairly time consuming and difficult. Give yourself a large portion of time.

Sixth Step:
Change the colors to those of which you wish to be the darkest of the doll's colors.
Be sure to do the different colors for different pieces(ie. a skirt, hair, shoes)

Seventh Step:
Fill in base.
I did not shade or do extra detail, but you may if you have the patience and other such things.

Eighth Step:
Enjoy!
CREDIT!!! Link to the original artist AND their work SEPERATELY.