Tons of people asked for this, so, I provided.
Learn to turn this:
Into this:
1. Find yourself a good manga scan and crop it down to the part you want to use in the icon. Fiddle with the brightness/contrast if it needs cleaning up.
2. Create a new layer between the background and lineart layers. Set the lineart layer to "multiply" and begin coloring on the new layer.
3. It should end up looking something like this:
4. Now, to color her vest. Add another layer above the lineart layer. Select the black area of the vest and go to Select->Modify->Contract, contracting the selection by 2 pixels. Then, fill the selected areas with red, on the new layer.
5. The red has seeped into her chin and zipper, which looks really weird. Let's erase that.
6. On the background layer, add a nice little gradient.
7. Now go to Image->Image Size and scale the image down to 100x100.
8. Go find yourself a stained paper image and make atexture with it. Or, use this one:
9. Set the texture layer to Multiply, as the very top layer.
10. Add a stylish border and you're done!