I forsee a lot of smudge, liquify and lots of uber painting in your future. Look up "Digital Painting" techniques. Tons and tons of tutorials out there.
Honestly though - the techniques you would use to create that image using traditional media are the same in Photoshop (it's just less messy and there are levels of undo). Shading, color and line. I don't know if you are drawing the image or if you are manipulating a photo - each starts differently but similar techniques are used. There are tons of Photoshop "horror" tutorials out there. Google it and you will find all sorts of answers. Try sites like www.3dtotal.com or www.deviantart.com and ballistic publishing. Have fun!