This is how I started. Using a fairly large paint brush set to a low opacity I quickly sketched in a rough form.
I then tightened up the Orc, still concentrating on the underlying form, not worrying about armour or clothes. I tend to work in quite heavily and then drop back the opacity, then create a new layer and work in again.
Next I put in the armour and clothes roughly, you can pretty much see the picture coming through at this stage. At this point I also flattened my working layer (not with the background, that causes headaches) and put a heavy blur on the whole thing. This is to stop me getting too tied down to the lines. By blurring the image I'm forced to rework. This stops me fiddling with details before I'm happy with the basics
It's then a matter of tightening further until I get something I'm happy with in the above WIP (work in progress) you can see white cut lines running through the legs. This is where I've used photoshop to grab sections of the painting and move them. I try to keep the painting fairly loose and open to change as I'm working. If you look at the earlier WIPs, you can see the arms and legs went through lots of changes.
It always takes me a while to get used to working with the graphics tablet again, I think what bugs me most is zooming in and out. With a sketchbook this feature is accessed by moving your head nearer and further away from the page, with photoshop you have to press a button. My photoshop has a glitch where it jumps to a zoom of 12 pixels, drives me up the wall. On the flip side, when I'm using pencil and paper I often start thinking ctrl Z but of course there is no undo.
I think I'm going to go back to paper for a bit with the orc. I want to think through the armour a bit more. I'm considering having a version with leather armour, and another with more heavy metal plate armour. I also need to think about weapons.