Agni - WIP and 'How to?'

Here's the process I used to make the portrait.

I used the GIMP to edit the original - Just brightness/contrast and then 'posterize' to the number of colours I want to make. If it doesn't look good, repeat with different settings in brightness/contrast.
Once I'm satisfied with the result, (trust me, I've spent about 3 hrs just to get it right) I then traced the outlines on a paper - A separate sheet for each color (Mirrored first).
Now I glued the papers onto the color sheets and started cutting them out.
You can figure out the rest I suppose

Here's the finished one: [link]

PS: I do not own the original image used. It belongs to the Vimanika Comics.