All the figure studies are looking good. I feel that the best way to study the human form is by doing life studies. Try finding some life drawings courses where you live. Then you also meet and chat other artists.
Value relationships in your paintings make them not work. They're all different colors, but middle values. Makes them flat. No depth. The lights that you use are in the background sometimes, which doesn't work. Your lightest light should never be in the deepest spaces.
You'll have to do simple value studies with white spheres (ping pong balls? White billiard balls?) and 45 degree lighting. Also do cylinders and other simple shapes. Wrap the core of the shadow around the shape.
Once you get that cooking, you'll be ready for the next step.
Wonderful sketchbook you're starting here! Keep pushing with tones studies.
You're already really great and showing lots of potential for even more! Loving your use of colors, in enviroments especially, actually eviroments seem to be where you're at your most confident in general. That's quite unusual and really awesome