I'm definitely seeing improvement. Especially in those various Mimikyus!

I would say target body proportions. These are hard, and yes, trust me, they've been my nemesis for a while. I still struggle with them sometimes. The big thing that helped me was to look at reference pictures while sketching. Such as when you draw Umbreon, look at an official Umbreon picture that has a pose at least close to what you're aiming for. I also do two sketches before doing final linework. The first is very rough and is mainly to get body proportions right with basic shapes. The second is a refined sketch to really get an idea of how you want the final details to look like. It may seem like overkill, but it helps immensely. And yes, despite the number of times I've drawn Pikachu and Emolga, I still refer to reference pictures of those two. That will usually nip proportion issues.

Give it a try and let us know how it works out. :3 But overall, if you keep working hard at this stuff, you'll be rocking out great pictures all the time.