Looks darned good to me!

Very nice. One slight critique is that the rear of the Rhino is further away than the head. Because of atmospheric perspective, you want the opposite line weight. Thicker with objects that are closer to camera and lighter for objects further away.

I think these look pretty good. Here's some advice I have for you. It's not that you want to picture two stacking balls, but you're using this exercise to improve your gesture drawing and observation. I think how you approach each figure is situational. In some cases, it may help to draw in the line of action to capture the whole movement from the get go. In others, you draw the ball, then you will draw the connecting contour line and wrap it back into itself to really show that pinch. It is situational in the way you see it. Also, most of the time you'll want to avoid the snowman effect, which is having the overlap show on both sides. In some drawings it is completely appropriate (I see one in particular you've posted here). Really pay attention to the centerline of the figure to try to interpret which way the masses are bending and twisting. Hope that helps.

I feel like you keep improving when I see your work. There doesn't appear to be any obvious perspective issues as far as I can tell. It looks pretty darn good. As for painting, you have good values, core shadow, primary, secondary, and fill light setup going well. I think the only thing missing is atmosphere which is pretty much the next level in digital painting. Putting up effective backgrounds, using compositional elements, and using colored/bounced light, elements such as warm/cool colors, aka color contrast (which I do see some of it in this work), atmospheric perspective would make it more complete. Also could use some texture such as scratches on the metal. Some material studies I'm sure would help a lot. I am not at that level myself, but it's something I've sort of mapped out in my learning and doing texturing in 3D also helps me understand some of these concepts.

Looks like your working digitally so you could do this using layers. If you didn't you can still use a kneaded eraser. But first, try getting the gesture down. Then drop the opacity or erase lightly so you can barely see the gesture drawing. Then add your shapes on top. I personally like to throw some perspective lines on the ground plane to help me see the space my subject lives in better. Then draw your shapes on top of it. Start with the 3 biggest masses. Egg shape for ribcage, egg shape for pelvis and egg shape for head. Then fill in some cylinders for the legs. After the primary shapes, then work on the 2ndary forms. Simple to complex. Draw through, and don't be afraid to erase and clean up lines as you work. A dog is a difficult subject because everyone is familiar with how a dog looks and there's fur and other things that could make it hard to draw (although this one isn't bad). People will pick out problems very quickly with every day subjects. Try animals with no fur and have as basic structure as possible to begin with, like a hippo, rhino, reptiles, etc. Hope that helps.

It takes courage to put up work, especially as a beginner. You're doing fine and will continue to improve with practice. Good job!

This kind of reminds me of some Dave Finch or Jim Lee where they describe roughing in muscles like little footballs.

very nice job.

That's very lovely. Getting some Frazetta vibes.