Before we begin:
Start with an editable mesh.
Detach by element:
Using detach/element, break the model apart with two goals in mind:
(a) detach by area of the model (head, torso, arms, legs, feet, hands) and
(b) detach by direction (front, back, left side, right side, top, bottom).
The resulting "selection groups" will each face a single directions, with as little curve as possible.
Note#1: The most difficult part of this stage is judging which polygons belong with which direction. Streaking in the final map results from polygons attached to the wrong direction (i.e., side polygons attached to the front).
Note#2: Because we are detaching by element, the model is still all one mesh. This is important.]
Make a morpher copy:
Make a "copy" copy of the model.
Put a morpher modifier on the original mesh and take a morph of the copy. This will allow you to return to the original shape at the end.
Hide" the copy of the model.
Note: Frequently test the morph (with subobject mode off!). If it dies, the geometry was changed.
Arrange elements to the front:
At the subobject/element level, pull the main model apart (remember to frequently check that the morpher still returns the original model shape).
Rotate side and back elements so that everything faces the orthographic front.
Collect the elements by area: put all the torso parts together, the head parts together, etc. It can help to also group elements that will have similar textures (i.e.,all the skin elements in one area, the shirt elements (torso and arms), etc)
Fit into tightest square:
Bring the seams of the elements as close together as possible (without overlapping)
Arrange the entire map into as tight a square as possible. This serves to optimize the space required for the final map.
At the subobject/vertex, select the entire mesh.
In an angled view, non-uniform scale to flatten the elements. If everything was arranged to orthographic front, this should be along the y-axis.
Apply UVW map:
Between editable mesh and morpher in the stack, apply the UVW map modifier (planar).
Make certain that it faces the front orthographic view (check the axis, be sure that the point is arranged "upward" and the green line is to the right), and that it is perfectly square (to be sure, switch once between spherical and planar mapping, to reset).
Return to 3D shape
At the morpher level of the stack, morph the figure back to the original 3D shape. If the morpher fails, geometry was changed and you likely must start again at step 2.
Collapse the stack.
Weld all elements back into shape. Shortcut: select all vertices in mesh and click weld/selected. Works if threshold is right.
Compile the full map with Texporter:
In the Tools panel, open the Texporter plug-in.
Change the settings for a square map (1024x1024 is a good starting place) with constant fill.
Export the map, and save.
Note: to texport subobject map colors, set up front and back lights and apply utilities/assign vertex colors.
Create the final art in Photoshop:
Bring the texported JPEG into Photoshop and apply the art.
Export as a JPEG, and drop onto the model.