Read and watch as much as possible. Horses are like people - they have personalities, thoughts, opinions, experiences, memories, etc. A method that works well for one trainer you see in videos may not work well for the horse you have in front of you. The horse in front of you may do well with a different style, or need a little mixing depending on what you're doing. The horse in front of you may be stubborn with some things and terrified with some others.
Most people won't try to intentionally steer you wrong, but they can accidentally do so.
* I'm often reading and posting from mobile and Siri loves to make a mockery of the English language.