George Washington was an intelligent man who had experience in land and fighting prior to the American Revolutionary War. Having this experience is what allowed Congress to have faith in Washington in order to lead the troops to success in the war.
First, George Washington surveyed land and he was successful at it. This means that he was knowledgeable about land which would benefit him when leading his troops across land. He could recognize different landmarks and directions.
Second, he led the militia in Virginia during the French and Indian War. At this point, his experience would prompt those in Congress to provide him with the responsibility of commander in chief of the Continental Army. This allowed him to prove his leadership skills to Congress.