Here is my general process from sketch to values. It’s not completely done. I still need to clean it up and make some corrections but it will do.
I decided to have the brightest light source kind of coming from behind him, which will be the sun, so almost his entire front will be in the shade. Kind of like the sun is starting to set behind him. After I’ve completed a rough sketch i start painting in my values by deciding on what the base value is going to be for each individual piece of clothing along with the other areas and paint on a new layer above my sketch. I decide what the darkest value is going to be and start it off kind of light and I make the lightest value pure white.
The next thing I do is use the lasso tool to make an outline and fill it with a light to mid value on a new layer and set it to multiply. Sometimes I just fill the whole canvas instead of making an outline.
After that I select my darkest value and make it slightly darker. This will become my darkest value and then I start painting on a new layer, trying to show some separation.
At this point I turn off the sketch layer, although sometimes I leave it there and just paint over it, and do a levels layer adjustment to make the values slightly darker. When you turn off the sketch layer you should begin to see separation of shapes through value. I move the sketch layer to the top and use it as guide when I need it.