CeltWolf13, I can explain for DarkJak.
Mirroring - A simple and effective technique to doing heads.
You just copy half of your head, since you most likely are working with the required size, 128 x 128, that would be 64 x 64, being the selection needed.
So, select the Rectangular Selection Box, and start from the top left corner and drag in to the right, 64 pixels. Then, drag it down to the bottom.
You then hit the following commands, in order: CTRL + C (Copy), CTRL + V (Paste), CTRL + D (Deselect).
Then go to the top, in the Edit Menu find Transform, then I assume there would be an option for Flip Horizontal. Move it so that the top right corner of what was just pasted is in the top right corner of the canvas.
Blending - Basically like a gradient to the back of the head.
So, if you have a pig for a head. And you for some reason want the back lighter than the rest of the head. So, say the pink used for most of the pig was Pink1, and the lighter pink was Pink2. In order to blend it efficiently, you need to make some sort of gradient from Pink1 to Pink2.
I hope that help just a tad.