I agree with Anna about studying structure and proportions using different dog skeletons. Such practice seemed rather tedious to me when I was a young artist, but really understanding structure is a price you have to pay for life-like art that makes sense to the eye, and it's better to pay up now than later since it will really improve your skills faster.
I think you demonstrate a feel for flow and action, which is awesome. Try to push that further to really capture the exaggerated motions. Try a few sketches where you make it really over-the-top extreme with curves, bends, sharp angles, then refine it back. It's a still image on a page, but a little emphasis and exaggeration can add a lot of life and motion.
I would also encourage you to use fewer reinforcing lines (line darkening) for your sketches and to use them to draw attention to important curves or plane changes. Dark contrast of heavy lines draws attention to that area, so try to not use it as a correction tool, since it will only bring more attention to a mistake or reinforce an awkward line, and those dark lines can make the drawing feel more stiff. Redrawing a line a couple of times is okay, we don't often get it right the first time, but work on lightly drawing long, single, flowing lines drawn with shoulder rather than the short, scratchy multiple lines that darken your contour (outline) so much.
You've got a lot of good things happening in your sketches, so just keep putting in your time and being thoughtful during practice and you'll go far. Thanks for sharing.
