That is great for just starting off! I can't really comment on anything but the horses as I don't do anything but the horses.
What program are you using? I hope I didn't miss this answer because I just skimmed through this post. I can say use bright highlights and dark shadows! It really makes muscles stand out.
Here are some examples that I've made to help with the making things stand out. #1
If you have any questions just let me know and I'd be glad to help any way I can.