Hi Marco - some possibly helpful pointers: check that you're counting the 2 points for the Siege token. Try to upgrade at least once, so you get the choice of card you need when you need it. Do this early if you're short of fleets, or the Common Sense/Declaration of Independence cards. Try to use fleets early, to get the British to waste cards, or at least delay them. Don't go for Canada, unless you get the right cards early and the British are slow there. Don't forget your Hamilton ability. Use Light Cavalry to get troops out of regions before you lose them. Perhaps you're already doing all this...
If you can discard cards to promote units, and if your cards tend to become useless towards the end of the game, does that imply that you're supposed to get out as many militias as you can in the early game, and promote them in the late game?
yes, but there is only a very limited number of pieces representing promoted units, and that's an absolute limit. So it has happened that I promoted everyone who could be promoted, and still ended up with useless cards.