There are several key factors which lead to the American rebels winning the American Revolution; however, it's important to access those victories by seeing the British and American war strategies.
Firstly, American had no naval power, nor a standing Army as such until the Continental Congress appropriated the Militia following the Siege of Boston in 1775, and turned it into what became a unified fighting force known as the Continental Army. Still, this rag-tag army suffered desertion rates throughout its campaigns, particularly after the initial rage militaire wore off, and was not especially threatening, nor well equipped or disciplined -- much to General Washington's disappointment. Still, Washington had war experience, given his dealings in the French and Indian War. However, the might of the undefeatable British Navy and its military was world renowned and worrisome. Thus, in the Northern campaign, Washington employed his famous Fabian Strategy which was employed to wear down the British rather than fight them since Washington had neither sufficient enlistees nor weaponry. Washington knew that the British's Hudson Highland strategy could be defeated, but not by using standard pitched battles.
Secondly, with the public entrance of the French (they'd been secretly supplying American arms from the time of the British invasion at Long Island,) and their navy following the Battle of Saratoga in 1777 -- a decisive American victory was all but assured. The British southern campaign, meanwhile, was rapidly disintegrating with Cornwallis and his army being lured into a maddening chase of Danial Morgan following the battle of Cowpens in 1781. Morgan managed to lure Cornwallis eventually to Yorktown, Virginia into an inescapable trap. There, Cornwallis found himself surrounded and outgunned by both American and French forces where he famously surrendered.