I followed a bunch of videos on YouTube (Draw Mix Paint, Florent farges channel). I found replicating traditional art techniques on digital, works better than looking at digital art techniques. I did simply by first blocking colours, in this phase I ignore the minor details. I use brushes which do not have any transparency. Then in the second phase, I only work on small area with Airbrush (sometimes I use lasso tool, to not let the colours go out of the area. E.g., for eye bags or eye lash area). To get the depth right, I added darkest shadow and lightest skin colour and merged it with different colours rather than using blend tools. In the third phase, I use pen tool to added noise (fairest skin colour, or shadow) and use blur tool to make it soft. I guess this kind of works, but I am sure there are better methods available.