-Have plenty of archers when attacking any fortress or during open-range fights. Whether you are defending or attacking, keep your archers bunched together and let them knock out the other troops. Do not try starting with the largest castle or fort. You can kill many attackers you can kill with just 150 archers stationed inside.
-When facing the second-largest wooden structure, take at least 100 archers and pull them around to the right side of the fort. There is a small notch where the land protrudes into the water. Have all your archers march to that notch. You can take out all enemy archers or other troops that attempt to shoot back when they get around the one o'clock position of the fort. After reducing most of the troops there, use a battering ram to knock down the door.
-While in battle, always try to flank. Also, have a least two groups of melee troops; one to engage and protect your archers from the front, as well as one fast group to go around and get the opposition's ranged troops.
-Always hire mercenaries when you can afford it. They are more effective, and you will not suffer morale or manpower problems (unlike an army raised from peasants).
-A bit of ale each time the cart comes around will keep your population happier. Note: You do not have to keep them drunk, just happy.
-If a province is losing about 160 happiness per season from taxes, the -160 happiness will rollover to about +120 happiness. This is shown directly in the tax box. Additional taxes will lower the 120 happiness. The only way to get -160 happiness for taxes is to have about seven provinces all at 50%. After the happiness rolls over, you have an almost infinite income and a large happiness bonus for all provinces. Note: The opposite will also happen, with 100 happiness rolling over to zero before increasing again.
To get ahead, have plenty of money and happiness of peasants. In order to do this, start the game by selling most of your cows and all of your crossbows. These are worth tons of money and provide start up cash for your goal. Purchase about 1500 to 2000 units of wheat and ration your food so that most of the consumption is of grain, and very little cows. After that, set your taxes at 6%, and buy lots of iron and a little wood. Make your blacksmith produce armor (knights), and sell them when the merchant arrives again. Repeat, and you will be very rich over time. Use the money you make for upgrades to castles, buying other weapons, buying mercenary groups, or more food for your peasants. This strategy depends on you building up your territory first, then striking out at neighboring counties. Another tip is to attack the center county out of an enemy's land that touches yours. This does two things. The first is you gain another county. The second is you will split his land mass up and he will actually lose control of more than just the one county. Be ready for retaliation.