Perhaps the most important precedent set by President Washington was the institution of the Presidential Cabinet. There was no provision in the Constitution for Secretaries of State, Treasury, or even an Attorney General. Washington created all of these.
Secondly, when Congress asked to receive certain information from the executive branch which Washington considered privileged, he declined to furnish it, thus setting the precedent of Executive Privilege.
A little known fact is that when Washington took the oath of office, he wore a civilian suit, not a military uniform; but he wore a sword at his side to mark his authority as commander in chief. The precedent set was that the president, although commander in chief, is not a member of the military. No U.S. President has ever worn a military uniform while in office.
Obviously, all of these precedents were wise ones. Washington knew that every action he took as President would set a precedent for future presidents, and acted accordingly. Both the examples set forth above have made the government more efficient and the executive relatively independent.