Just how I get things done on photoshop
1) quick sketch on layer 0 in a light colour.
2) Some lineart on layer 2! Attention is paid to line weight etc. For the rocks, how I get that sort of structured type of line without pen pressure, I draw a really thick one ( 12-15px), and then use the eraser tool to 'sculpt' it.
I tend to do this a lot, not just for structures but for people/tattoos etc. It's just done to get a painted type of effect.
3) I like to colour the people first, so terra gets a bit of spiffy earthy colours. This was done on layer 1.
4) To make the drawing more dynamic and to better establish the light source, i throw in a bit of gradient on layer 3. This is optional of course, but I just like to do this extra step because my shading isnt profecient enough for me to acheive the desired look without it
5) I used a very helpful rock tutorial to colour the chunk of rock terra's riding on![link]
Don't be afraid to look for tutorials or referances if you're not 100% sure how to colour something.
Aand yeah thats just a really quick jist of how I do things on photoshop.