To offer some pseudoconcrete suggestions:
The AI is presently ignoring targets of opportunity, and presents too many such targets. For instance --
The AI leaves unescorted, empty transport fleets at sea within easy range of enemy fleets for no obvious reason. A transport fleet that is heading somewhere to pick up troops should be defended, as should one that is carrying troops or providing invasion supply. A transport fleet that isn't doing one of those things isn't even good bait (because it is captured without forcing the attackers to stop), so it shouldn't be out there. In the worst case, it should be in a defended port.
The AI should not place a level-A leader other than Napoleon with any inferior leader, which is practically all unless we're talking Mack vs. John. It's of somewhat dubious value to they place them at all.
Great Britain should *always* block the channel crossing arrow. Enemy fleets there must *die* -- it does not suffice to block the crossing with a weak fleet that's going to need to be replaced the next turn. Blockading enemy fleets and killing any non-blockaded enemy fleets within range of the British Isles should be done -- hell, you have the money to keep the fleets at sea as needed. Build more ships. Sweden, Denmark, and Naples are minors of particular concern to GB. Holland, if lightly defended and the Holland fleets are still around, should be attacked if there are suitable minors to provide the boots.
Russia, if DoWing Sweden, should not march into Abo and cause the war to lapse unless it's firmly aligned with whomever's getting the Swedish corps and fleets. Which, for an AI, is not entirely all that certain.
Should an AI be about to lose a minor with an intact fleet to an enemy (say, French-controlled Denmark being invaded by the British), doing even an obviously suicidal attack with the minor's fleet is entirely legal, if not entirely realistic. The same holds for a minor army that's away from the minor that's about to fall -- might as well do something with it before it's lost anyway.
Prussia and Austria should NOT DoW each other, and should back down from DoW'ing each other, at least until France has been beaten down with an unconditional surrender, and unless the one issuing the DoW is already far stronger than the other. They bleed each other far too much.
AIs at war with each other for a considerable amount of casualties without a surrender should reach an informal peace. They're sitting ducks for everybody else if they continue. An AI that's far significantly below its previous peak head count probably shouldn't be DoWing other majors, as well.
It is presently safe to leave empty depots in front of even starving Turkish troops. As Spain (w/ an entire Ottoman Empire in 1807 or so... oh, and having taken Wales, Ireland and Scotland by then as well, without a single battle against any British corps or fleet -- just the garrison of Gibraltar), I landed 3 Spanish corps in Athens, then took Salonika. Using Salonika for incoming sea supply, I marched up to Thrace, built a depot, crossed Gallipoll, and besieged Constantinople (building another depot there).
I left the depots in Thrace and Salonika completely undefended. I didn't bother swatting the feudal corps who were scattered around ignoring the depots. Minimally, eliiminating my land depots would have forced me to use invasion supply, fed the feudals, and prevented me from reinforcing the siege without actually landing more corps (or marching Ottomans across Anatolia), and would have made it difficult for me to chase inland (away from the invasion supply). Win-win-win, and in any event sending individual units to hit undefended depots that are part of an enemy's depot chain would be appropriate -- especially for units that would otherwise be foraging, and don't have a battle to go to.
And as I've noted before, the AI appears to assume that any blockading fleet is strong enough to not challenge. To illustrate, the way I got an unconditional out of GB, as Spain, without a single battle (note: they and Prussia DoW'd me in Jan 1805 -- a bit dangerous for GB, and a complete waste of 4 PP for Prussia)... almost the entire GB fleet was in Gibraltar (although Nelson was on a single heavy fleet in the Channel), which I kept blockaded with most of my fleet (at first) and then a single fleet with 2 light ships. I besieged Gibraltar, whose garrison quickly starved -- but deliberately walked out without occupying the city in order to not force the GB fleet to evacuate towards my far weaker 'blockade'. The blockaded fleet behavior is particularly glaring because fleet strengths are known exactly and there are fewer variables and possible outcomes... and a blockaded fleet has nothing else to do other than attempt to break out.
I launched an amphibious assault with a single corps into undefended Bristol (ignored by the British heavy fleet in the channel, and the two British corps in London). My single corps garrisoned cities in Wales, Scotland and Ireland, then sat in Edinburgh until the British surrendered to me unconditionally, despite their not being pressed by anybody else, nor my lack of movement towards London.