Let's talk about the coloring process:

First of all, I want to say that the way I do the coloring might not be the best way, honestly: I think the best way to do it is probably to draw it in grayscale to set the value and add colors on top of it.

But the way I do it: starting from big and getting smaller and more detailed. 
(lower is gif of face coloring process, it's a bit heavy, give it a bit of time lol)




There are no big secrets, really, just rendering from big to small, but here are some things I do to make it easier:

(Reminder, I use Clip Studio Paint program).

1)Use a multiply layers to get blush or shadows more prominent if necessary.

2)Tonal correction is your friend: getting colors right is hard, so use Hue/Saturation/Luminosity, Brightness/Contrast, and Color Balance to get it right.

3)Try to use Blend Brush as less as you can.

4)I usually color one big part on one separate layer: if it's skin, I add extra layers only if I need to use Multiply or add some detail that I am not sure about (if I like the result, I combine them into one layer). I am, personally, not a big fan of many layers, because my file gets heavy and the computer just shuts down lol.

5)If I want to transform any part, I usually copy that part into a new layer, so in case everything goes wrong, I can always go back to the original. If I like the new transformation better, I combine the layers.

6)I generally copy the layer I am satisfied with into a little folder, so if something goes wrong, I can always return to the point I want.

7)Before, to make the skin a little bit shiny (like from sweat) I used Add or Add Glow layer setting, but recently I found a better way:

• Create a new layer above the skin layer, and clip it to the skin layer;
• Color it with pure black;
• Set it to Color Dodge mode (the black layer will become invisible);

• Take a brush with white color, use a textured brush instead of a soft one;
• Paint where you want the light to be;

• Change transparency if you need, and use Blend brush if you need.

8) Sometimes I use sharpen option if I want brushstrokes to be more visible.

I already did it before, but just to be sure I clipped the my main custom brush I use for almost every coloring I do as an attached file (also for Clip Studio). Also clipped the video of process, since the gif might not work on smartphones.

I hope it helped a bit :D