Yup, you're more than welcome to use whatever I post - it's all to help you out. ^^
So I think one of the biggest issues which make it hard to finish off is that your pose is a little off. Since our poor knight is feeling so forlorn he should be hunched over more, shoulders forward. I also bend his right leg to go under the left and dropped his right arm to the ground (which is now hidden).
Unfortunately he shrunk in this process.
As for as learning about lighting, I started doing value studies to help me out with that. Just draw pictures from reference in greyscale for an hour once a day and you'll be way ahead in no time (I really noticed a massive difference after a month).
Similarly for poses, just do pose studies.
Whoops, didn't shrink his head. Fixed.