And here is my last source (note that it was under v1.06 and that the AI has kept improving):
Run. Run. Keep running.
At least until 78.
I've been able to win on hard, but I suspect that's about to change with 1.06.
The key to the game is getting French and Spanish help as quickly as possible. That means that you need to try and maintain 1 or more strategic cities in each Region. If the British have an entire region, it's 15% less chance of French intervention. Letting the British get 2 regions may be irreversibly fatal.
I leave the Deep South to it's fate. Only options are to siege outlying positions and try and prevent the British from having every city. Even with Cornwallis and a few reinforcements, they don't have enough men to adequately garrison everywhere. Provided you don't get caught by Tarleton or other roving bands, you can usually win a city back, and force the British to find another regular unit to garrison it with (that all takes them time, and you'll be somewhere else doing the same.
Having said that, my current game saw Cornwallis land in New York. The Deep South is entirely mine, and the north is a death trap, so your mileage may vary.
The South Central tend to be quiet in my games until late. There are too many cities for the British to do anything about you, and they tend to not have enough troops to take more than a couple anyway, provided you keep Howe and the Germans up north.
I used to work near Morristown and visited the Contintental site several times. Until playing though, I often wondered what the hell Washington was doing out there The British tend to march through, so I find Easton to be a perfect depot site and place to keep the army intact. From there you can hit detachments trying to take Wyoming, retake Phillie+Manhattan, and run back to Easton. You can tie 2 British armies up in this region if you're lucky.
North New England and Canada
For me, the key to every campaign in the game is Albany. If you can hold Albany then the British have logistical problems, can't ever unite Burgoyne with the Germans or Howe/Clinton, and can't move out of New England. That keeps South Central safe, and allows Washington to maneuver the Middle States.
Albany is well protected, if you hold Dayton, then the British can't use it for supply. Holding (and retaking whenever empty) Battlebro and Pittsfield will prevent the New England force from being able to walk in. With it's depot and horrendously short campaign season, Albany should never fall.
After Albany, I try and hold Norwich. It's a nightmare for the British to take, and when they move their army north, you can send some raids south into Southern New England:
I don't know if there's a rule, but it seems that Boston triggers many more colonial militias and Continentals to form. If the British army is off hunting you in the Middle States, and stalled in the North, then a capable force can retake Boston, Newport and Hartford. The British tend to react angrily to these moves, so be prepared to run, and don't disperse. Better to abandon every city but Boston than garrison and allow the Brits to siege you one by one.
Provided you avoid battle, don't get unlucky and run into 20,000 Germans, and prevent the Brits from holding a region, by 78 or 79 you'll be strong enough to start threatening them and fighting pitched battles. When the French arrive, it's fairly straightforward to maneuver and fight, or better still, trap the British in sieges. You still need to be careful as British quality will still see off all but much larger American armies.
Other things I do:
When you are going on the offensive, then it's faster than lugging supply wagons around with every army. A select few can supply the whole of New England and Virginia.
After the yearly disbands, send plenty of 1 star leaders off to likely recruiting centres. A regiment suffers a 50% penalty without an officer, and they tend to arrive in clumps. Campaigning season is short, and you need to concentrate those forces as quickly as possible.
GW is a skirmisher, but if his forces outnumber a British army, he'll fight it even if the quality differential results in the complete destruction of your army. Don't group too many units under his command, and he'll instead look to retreat from every battle, typically with no loss. I lost a game very early when GW stood and fought. Our "victory" destroyed the entire army and barely scratched the Brits.
They can be a pain in the ass, and sometimes supplement small British regulars. Although it's a brutal tactic, I try and exterminate them from the outset. Morgan's rifles, or Marblehead are good independent leaders and their 1 unit is generally enough to assault any Indian village. After you burn it to the ground, they don't come back next year.
I don't like tying up precious artillery in a fort, so I don't tend to make one. I've been able to defend the Hudson with hit and run sieges after the Brits move on. But, this might be impacted by 1.06. If the British are more efficient at rolling up 1 unit defended towns, then it may be necessary to fortify and hold with a garrison. WP is harder to take logistically, though Manhattan is surrounded by empty areas and is also a challenge. It will be interesting to see how these areas are handled with the new patch
One of the goals is to gain more units each year. That can be accelerated by not suffering disbandments, charasmatic leaders can help keep the army together, thus grow faster with the next season's recruitment. Washington and Arnold are good for the large armies, but don't neglect small detachments. Try to get all your charasmatic leaders employed somewhere. Keeping an extra 2-3 regiments per year may not seem like much, but by '80 it makes your force overwhelming.
Pulaski should go wherever the cavalry is, Kosciusko whereever you want to siege (or hold.) Sad irony, that two of the most congested stretches of road on earth are named after these fellows
Use other leaders where their attributes help. After playing the British for a while, it's nice to have decent leaders, and they can make a small but significant contribution. Fast Mover is very useful, especially for ferrying troops or supplies between armies. It only takes 1 fast mover to get the bonus, so lump them with larger forces when needed.
More than anything else, once I started to pay attention to command limit I had success. Everything from speed of movement to combat is affected. I'd rather have fewer troops than exceed the command limit. With American leaders there should be no excuse to let any group exceed command for too long. Much more a problem with the British, as it forces people like Burgoyne and his slow moving subordinate on you for the entire game!