What was one difference between the British and American forces at the beginning of the American Revolution?

The British army was a uniformed force that marched in relentless formation. The bulk of soldiers in this formation were not intended to fight so much as absorb the bullets of enemy forces until they ran out of ammunition, leaving them vulnerable to Britain's superior numbers and armaments at the formation's rear. This was a very effective strategy against the similarly-equipped French of the same period. Plus, they wore fresh uniforms and powdered wigs so they knew not to shoot each other by mistake.

American troops were largely irregulars. They hid behind trees, wore farmers' clothes, and shot from concealed positions. The officers were, with few exceptions, former British army regulars who had made their bones in the French and Indian War a decade or two earlier. They knew how British formations worked and what their limitations were, and that their best hope was to fight a different sort of war from what the British were planning to face. They also had "home field advantage", or better familiarity with the local terrain.

Some excellent examples of British tactics can be seen in movies like Kubrick's Barry Lyndon and the British television series Sharpe's Rifles starring Sean Bean.