>1 - cutting shit
The easiest way to go about it is to use the free select tool to select the part you want deleted. If it intersects or overlaps the main figure leave some room for fixes.
Then just use a normal brush to go over the outline and adjust it as needed.
If the line is somewhat straight you can just use the copy tool to copypaste the line around it for parts that are fucked or just don't have a line.
Keep zooming out to 100% while working to get a better view. Sometimes something looks wrong from close up but it's not too bad, or vice-versa.
>2 - cutting shit with flat colors
Same as above, except now you have to care about repainting stuff.
You can just use the brush most of the time.
This pic is a jaypeg though, meaning there's artifacts. A quick way to deal with this is the clone tool, to copy the imperfections of the compression. Keep in mind that the clone area moves too, if the area is too small keep clicking instead of clicking and dragging as you would with a normal brush.
>3 - cutting shit with gradients
Gradients aren't that bad to deal with. Just start with the general color by either using a brush or the copy tool.
When you have a rough mess use the heal tool to blend it all together.
The more abstract the gradient is the more sloppy you can be. Something like skin or hair requires a bit more care than backgrounds.
>4 - cutting outlines with different colors
Legoman often uses different colors for different characters, e.g. the girl having a black outline and the guy having a blue outline. Some artists do this too but with different colors.
Just use the brush/free select to remove the stuff around the lines you want to keep.
Next select the zones with different colors and right click -> colors -> colorize. For grey you just slide the saturation over to zero.
It might require some extra tinkering afterwards for the line to look good. Using colorize again on a smaller area, of going in with a brush works.
In this case the hand by itself looks kinda weird, fixing it would require redrawing and I'm shit at it. Just cropping it out works well enough in most cases. You might think it looks bad when compared to the original pic, but it's often really easy to not notice by itself.
>5 - bleach
First just select a small area to start with. Create a new layer, set it to dodge, and create a mask from the selection.
Paint the layer as any color with the bucket tool then use colorize to select the proper color. For brown to white you usually want the hue bar to be around 1/4 from the left, between red and yellow. Then mess with saturation and brightness as needed. Sometimes the skin is too bright compared to everything else, that can usually be fixed by lowering the saturation.
After you're happy with the color (it doesn't have to be final, you can still fix it later), it's time to mask the entire skin. As a rule of thumb if the shape is straight the free select tool is better, and if it's round a brush is better. Sometimes it's a good idea to use both, selecting an area with the free select to only modify that area, then using the brush inside the selection. Use black and white colors (in gimp you can use ctr+e and p to quickly switch between them) and work on the mask, don't modify the layer directly.
Dodge doesn't usually change black or white colors. If the outline is black or white you can just go over it.
If an area is somewhat messy, like a transparent zone or a fucky outline like the fifth pic in >>1621
, use a brush with less hardness for that soft edge.
If you want to change the color don't just colorize it again, go to colors -> hue-saturation. That allows you to change modify the current color instead of resetting it.
And always remember to zoom out to check it looks good.
If some parts looks particularly bad click the eye icon to hide the layer and compare it with the original. Sometimes some defect or part that looks bad was actually there in the original.
Something I didn't use in the video is extra layers. Sometimes you can't get the color quite right, in that case duplicate the dodge layer, change the new layer to soft light and change the color. It's usually good to use red, yellow, or white for a bit extra color.
And that's pretty much it I guess.