Some British tactics were OK, some were foolhardy. But the overall strategy set by the top generals was incoherent. Both Burgoyne and Howe made major mistakes in the first years of the war. The British never really recovered from these errors.
The other problem was that all soldiers, and most supplies, had to be shipped across 3000 miles of ocean. This was enormously expensive. The American forces could recruit soldiers locally.
The British Government considered America British territory and therefore assumed that basic supplies could be obtained from there - and mostly they were. Contrary to American mythology, there were plenty of local Loyalists who joined up.