Step 1:

Pretty obvious butttttt... draw the pic, etc. XD
Imma use the oekaki Im working on right nowwwww~ ^___^ it's of Mariah_pie_starbucks, moohahahaz >:D
Step 2:

Go to layer 1, set the mode to MULTIPLY. Got it? KAAAAAAAAAAAY! Moving onnn~
Step 3:

Begin to color your pic. OMG THE OBVIOUSNESS XDDDDD
Step 4:

OKAAAAAAAAAY! Now to shade! Shading is fun... eheh. XDDDD Find a color that's a LIIIIIL darker than the one you chose
for the skin. Use the AIRBRUSH tool to shade in the parts that need to be shadedd. (Duhrrrr xD)
Step 5:

Now, still with your AIRBRUSH, get the color white. Set the opacity a LIIIIIIIL lower so the white doesnt go overboard.
Ne? Got itttttt~?
Step 6:

Now shine the parts that needa be shined. (its time to SHIIIIIIIIINE! XD)
Step 7:

Now its time to ERAAAAAASE all that messiness xDDD MAKE IT NEAT, MISSY!! *ahem* or.. uh.. mister. XDDD
WEEEEEEEEEELL, that concludes the end of my tutoriallll~ wow, that was short XDDDD I hope I helped in some waaay~
If I didnt... you can throw fluffy pink pillows at meh if jah pleaseeee~ x]