Yeah, I find those “How To Draw Horses” books completely useless. I hate the circle technique. I found that the way to learn how to draw horses is to keep drawing them. 
Yeah, I referenced a couple of times, but it only turned out looking good once, but that was a while ago. Maybe I should try more referencing. I’d really like to know how to do muscles and other stuff. 
I tried that method too, just keep drawing. I can tell you most of a horses skeleton structure, and alot of the muscle and tendon structure, and I still can’t draw one. Le sigh
-hugs all around- You’ll get it 
Just keep trying! It has taken me about a bajillion years to draw things that even remotely resemble horses… (or horse-shaped blobs, rather… XD) But if you’re determined, and can find the time to practice, you’ll be well on your way ;3