In any yoga teacher training there are basic teaching tools that are introduced and extensively practiced: instruction, demonstration, observation, adjustment and assisting. Along with those, usage of language and voice goes hand in hand once we dwell in the instruction part of teaching yoga as well.
Why are those principle tools fundamental?
Each of those tools addresses more or less effectively a student’s learning style. Basically, this means that each person learns best through techniques that favors one mean of communication or (most frequently!) a combination of those means.