Hi, blue-cat, great work on the pictures! It seems that you have a rather good grasp on anatomy from what I can see.
But a rather 'good grasp' is not quite enough though. You'd need to be able to put all of those concept on paper in a way that makes the character not flat. Now then, I don't know how much you used the eraser or how you feel about them but I really suggest to use them more.
I know that many art teachers might say to put the eraser away but I think on the contrary. The eraser is, in my opinion, a good tool to use in order to form and build the structure of a drawing. I think that when the teachers mean to 'put the erasers away' means to not use it to correct mistakes but makes it a bit of all or nothing.
So here's the problem I have with the drawings but please be reminded that this is just my opinion and I might be wrong because I don't really know exactly what you're trying to do here.
You see, I think that the lines on your picture looks, rather uniform-ish. t really makes the character and the cat on the second picture looks like they're just stickered onto the floor rather than actually existing in a 3D space.
Also, from what i can see, it seems that you might have worried about the lines more than you worried about the form. Again, I could be wrong but it seems that when you were drawing this you were thinking about 'lines, lines, lines' over and over in your head.
Now, this might sound cheesy but unlike the first sketch, the second sketch has the character being in a 3D space and I found that when you're doing that, you need to figure out the picture as a whole instead of one by one.
Thumbnail drawings are usually a good way to plan your composition and see how things work with one another. Also just by seeing the second picture, I could feel that you were building everything around the character instead of everything around an idea or a concept. The point is, a picture needs to tell a story/idea/feel that you want to convey instead of just 'studio photo'.
But even a studio photo has a story! What is the photo for? Why is he wearing that clothes in the photo? Why did he bring his cat? You know, it's all about what it is you're trying to convey.
Like in the first sketch, Why is his left arm placed in that way? I don't really quite get it honestly. I can tell from the first picture that you got anatomy down but what you haven't gotten is how to project that with a context.
And the context is: the rest of his body. Even when you're drawing half of his body, you'd need to be able to know where the rest of his body goes (This is the reason why I always need A BIGGER CANVAS). But say that you don't have a bigger canvas, what do you do?
Well, you guessed it: Thumbnail drawings! Try to, draw a little picture of him, smaller than the final art of course, and then box it in. Then when you upscale it, even when you can't put it on the bigger canvas, you can see on the small one where the rest of his body goes and that might help you picture the piece better.
But of course, you might need any of this if you're drawing directly from life. But I get the feeling you didn't draw this from real life... But regardless of what you did, let's talk about the next topic: lines
"lines, lines, lines"... FORGET ABOUT THEM! They don't exist! They're just your imagination! (literally!). If you see a picture, like I said before, you need to tell the whole story and 'lines' are definitely not the whole thing.
Try to draw in 3D instead of 2D is what I'd say. Think of the depth. DEPTH!
And that brings me back to the point of erasers. Don't be afraid to erase! That canvas of yours, is meant to be dirtied, crumpled, thrown upon, err... actually don't do anything beyond dirtying it...
So try to draw even things that won't be visible into your canvas as well and then erase them later. Remember that eraser is your friend :)
But on the other hand, don't get wild on the eraser! If you happen to be rubbing on the picture, then that means that you are not doing it right. Erasers are used, not to correct a mistake, but to clean things up. So if you are rubbing then you made a mistake in using the eraser.
Well, that's pretty much it for now. There's sooo many things that I can talk about but this thing is getting a bit too long for my liking. So, for now, try to work in your perception of depth etc. before you'd go further is what I'd say. There are still MANY problems with the pics that I want to address but for now, these should be 'enough'.