This started out as "light" version of Jim Talbot's method to flatten a face and apply a decal but it's already running long...
Episode 1 is on Youtube. How to flatten a face?
errata: at about 5:35 you can see a bit of distortion happening on the screen-left edge of the mesh. That is because those patches are right next to the hidden stretched patches. Those will decal oddly at that edge. Ideally we would have one more column of patches between those and the stretched patches to hide and exclude from decaling. Then none of the decaled patches would be adjacent to the stretched patches.
Episode 2 is on YouTube. Fixing the overlaps.
errata: at about 11:30 I say "This character has a very long protruding feature in the nose..." when i really meant the chin.
Episode 2 Addendum is on Youtube. About those hidden splines in back
Episode 2 Addendum-da-dum is on Youtube. Not strictly required viewing, but this covers some more examples of re-apportioning patches for bitmap coverage.
Episode 3 is on YouTube. Capturing the wireframe, sizing it correctly, and painting on the decal.
Episode 4 is on YouTube. Discussion of what we need in a paint program. You can skip this if you are already quite familiar with AdobePhotoshop.
Episode 5 is on YouTube. We finally paint our color map.
errata: at about 13:50 I demonstrate a very soft brush but the screen capture loses most of that softness. You'll want to experiment with that yourself.
Episode 6 is on YouTube. Bumps and Displacements.
Episode 7 is on Youtube. Controlling hair with a map.