What kind of opacity setting I use in Digital Painting ?

What kind of opacity setting I use in Digital Painting in Photoshop and Gimp? That is one of the most asked questions on this blog.

MS: Believe me, i've watched all of your videos, and i got really inspired.
I bought my graphic tablet about a few weeks ago and i've been experimenting, checking youtube for more tutorials.
I found yours to be most helpful.

1) What kind of opacity setting you use when you paint in Photoshop?

Xia: First, I use low opacity (30-50%) to find values and move shapes/shadow around. It's kind of similar process when you sketch with pencil, you have to get a rough draft or construction lines and rough values (shading, lighting)
After I get what seems to be underpainting (close to corrected values) then I use only (70-100%) and be precise of where you put your paint and strokes using 100% help keep your color clean and not muddy. Then just use logic and intuition where to fix and use opacity according to the local values and decide whether you want soft of hard edge on that area.

MS: 2) But what confused me is, after your sketch you started on the shadows. From what i was taught i should create a new layer and set the sketch as an outline.
From what i can can tell, you used the same layer and changed opacity of the brush to make the shadows.. same for the actual painting. i need heavy tips :D

Xia: What I usually personally do is create another layer on top or under the outlines layer to paint values (shading or lighting) in the beginning. Then as it progress in to form that I want then I will forget lines, think shapes, values, and edge. If you want to add line art, add it after the painting process is done. (Unless you have scanned in inking lines as separate layer, you should put it on top of everything at all time and painting under. In that case, it shouldn't take you long to paint, just get the basic values and colors or you can push it more toward painting if you like because you want to show off the line work. if that make sense.)
then again i'm an amateur when it comes to digital painting =/

Good luck