I agree with just sitting and watching horses interact and how they behave, HOWEVER what we sometimes think we see, is not how horses see things and there may be some things you have previously been told by someone which might not be correct and might influence your thoughts, then your words, then your actions. We are predators and horses are prey, so often what we think is the opposite to how a horse thinks.
Personally, I like Rick Gore. Many do, many don't. But he has a website filled full of info and the videos on youtube have great info, especially the herd behaviour ones. He explains herd dynamics and what and why horses do things, why they stand a certain way, how and why they react to different situations etc. He debunks alot of the popular do's and don'ts in the modern horseworld aswell. He has a no BS approach to horses and nothing is sugarcoated so don't expect anything 'nice'. He tells it like it is. horseawareness's Channel - YouTube