One minor general strategic hint (useful in all strategy games actually):
Try to take out the enemies ability to keep on fighting (i.e. recruit more troops) as fast as possible.
Here this means try to locate the enemies fortress and take the province it is located in as soon as possible (vs AIs this is the key to victory IMO since they only build 1 fortress).
You don't even have to take the fortress itself, just holding the province prevents the building of new troops (there) and usually nets you a very nicve additional income which you enemy will no longer get (getting stronger while weakening an enemy is always a good idea
).
CharonJr