Friedrich von Steuben came to Valley Forge during the time when Washington’s army over-wintered there.
By the end of the spring of 1778, he’d turned the Continental Army into a highly-competent military fighting force.
He was effective because he had expert knowledge, high standards, and the expectation that the people he trained were capable of becoming great. He made sure that the people were well-trained (lots of practice), and the rules were standardized (written down in the “Blue Book”), and those rules applied to everyone (rather than having each regiment/team doing it a different way).
What is especially impressive about his success is that von Steuben was able to do this in less than 6 months… while not being able to speak English. He used translators (many of Washington’s army, especially some from Pennsylvania, spoke German) and he displayed charismatic gestures, pantomime, and body language to get his points across. Also, he did not just say “do it,” he (and his translators) explained WHY to do it that way.
His training built up morale and confidence—the soldiers began to see “we can do it!” in their actions.
And his “Blue Book” has been the basis of American military training ever since.
(image: https://allthingsliberty.com/2013/05/impact-of-von-steuben/)