For this tutorial I'm using Gimp 2.2 so your locations for scripts and filters might be in a different location.
Visit this site and download the pack of scripts and install them before starting Gimp. The download box is outlined in red towards the bottom. Browse through his post for some information regarding the scripts. The script you mainly need is the one called "cutout".
1. Start Gimp and open the photo you want to edit. Do your cropping and any cloning or flaw correcting now. It doesn't have to be perfect (if you use clone and smudge and your smudge lines show - no biggie). In my photo, the dog had a red leash attached to him.
NOTE: You can simply just use the cutout script-fu and call it done, but I prefer a little more outline, or edge, occasionally in my image. Just experiment, it's how we learn new tricks. Everything I learned is from trying tutorials, even if I'm not after the instructor's end picture, since one photo will provide slightly different results than another.
2. Duplicate your layer once so you have 2 layers.
3. Use the cutout script (Script-Fu> Artist> Cutout). I used settings C-11 and S-8. [Thumbnail #2]
4. A new layer called Cutout is created, hide it by deselecting the eye in the layer box, go to Select> None to get rid of the marching ants around the image.
5. Desaturate the 2nd layer (Layer> Colors> Desaturate). [Thumbnail #3]
6. Layer> Colors> Invert 2nd layer. [Thumbnail #4]
7. Change layer mode in layers menu box on the 2nd layer to "dodge". It should have some wild popart colored thing right now. [Thumbnail #5]
8. Select background layer and desaturate. Results can be pretty cool, I sometimes save this really quick then continue on. [Thumbnail #6]
9. Select 2nd layer and apply a Gaussian Blur (Filter> Blur> GB). Settings based on your taste. I used 5. [Thumbnail #7]
10. Select background (bottom) layer and oilify (Filter> Artistic> Oilify). [Thumbnail #8]
11. Make sure the colored layer is still hidden (you'll have 3 layers and 2 eyes showing in the layers box), then Image> Merge Visible Layers (I use default settings, hitting okay - DO NOT flatten). This is another image I occasionally save before I move on.
12. Move the cutout layer to the bottom of the layer pile by using arrows in the layers box. Make visible.
13. Change the layer named background to layer mode "overlay" and then duplicate this layer.
14. Change the opacity of the copied layer to your taste, I set mine at 30%.
15. Image> Flatten. Now save.
My finished photo is below. I believe you can click on both of my images in this post to get a larger view.