You've definitely improved especialy at muzzles. Over the time line you can see some major improvement overall. One thing I would suggest is taking a page in a sketch book, and doing one thing over, and over. Draw an eye 30 times on one page, or a speed sketch of a horses head/hoof 5 times on one page. Doing sketches repeatedly like that can help you drill yourself on proportions or shapes. Another thing I would suggest is flipping your art upside down while you're working on it. You'd be surprised at what kind of flaws you'd find when you turn your work another direction.
Other than those you're getting visibly better with each work, and I don't see any help in pointing out proportion issues when it's clear you're already working on them.