This colouring style will give these kinds of results:

Final

Screen/Multiply was the very first colouring (CG) technique I learnt.
Essentially, it's like painting, but instead of going through the colour picker and finding the colours, it adds a blending effect to your brush, so that whatever colour you are painting with, will appear either lighter (screen) or darker (multiply).
So, as with the other colouring techniques, grab a picture and fill in your flats.

Flats

In this tutorial, I will be using my Little Demon picture, and will be painting his head.
Grab your Lasso and select the area you want, or if you want to paint on the whole layer, select the layer contents (CTRL+Click on Layer Thumbnail), in this case I selected the layer contents of 'head'.

Selection

Now that you have your selection, you need to grab your brush tool (B).
Look at the top of the screen to see the options for the paintbrush. The things you want to look at are the Mode, the Opacity and the Brush Size.
Depending on how you want it to come out, you would want to change your brush radius/weight, so just experiment with a few different ones.
In this tutorial, we will start with a large, soft brush, and we'll start with the lighter shading.
Change the Mode to Screen, and the Opacity to something low, I used 19%.

Screen

Start painting where the light would be shining on his face.

Lighter

Once you're done doing the lights, start with the darks.
Change the mode to Multiply.

Multiply

Darker

If you want more detail, you are going to have to make manual selections around certain areas, between lines, in this case it was around his brow.
This is how it turned out.
I personally don't use this method, but it can produce some really good results.

Final