This is my first drawing in PS, lineart and everything was done in PS, mostly just using default brush, smudge, and opacity. I drew it from life it's a stuate I own. It's also not complete, haven't rendered the hands in.
not bad for your first time drawing and painting in ps. My first suggestion to you is define your light source. Right now you have highlights and shadows but they don't make any sense. Take advantage of the fact that you have this figure in 3d. Maybe get a desk lamp and shine it on him with all other lights turned off.
Also, consider maybe a more neutral background color. The black is overpowering the figure at the moment.
As far as Photoshop tips go, it looks like you're using very small brushes which makes it difficult to render volume. As a general, personal rule of thumb, I try and use the largest brush possible when rendering something, until it's too large to fit in the area that I'm trying to work on. But that's just me.
Also, if you're not thinking about this as a polished, finished piece of art, treat it like it is. Think about the composition of this. Do you want a really tight frame around the figure, or do you want looooottttssss of space around him? Simple decisions like this can dramatically change an image and make it more interesting.
And also, the collar-majiger seems a bit wonky. The side that's going behind his head on our left seems to suggest something that is round but the side on our right is very angular. I dunno though, cause I don't have the figure in front of me, but, a double check maybe?