Killing enemies and selling their stuff as loot and their prisoners - thats the lategame ways to earn money.
How much income a village/castle/town generates is determined by it´s wealth and prosperity, and in case of towns, by the amount of caravans and farmer parties coming and going. Advise about that special topic is around plentiful, simply look it up. There´s a reason why a search function is implemented on this board.
But back to your question:
Hand out land to vassals to lower your diminishing tax returns - as I told you in the other thread, look it up yourself via the mighty search function to get answers such as these:
http://forums.taleworlds.com/index.php?topic=179597.0
http://forums.taleworlds.com/index.php/topic,188133.msg6563516.html#msg6563516
http://forums.taleworlds.com/index.php/topic,174503.msg4191750.html#msg4191750
Read them. Especially my post in the last link to get the basic clue of your problem.
Basically it´s you´re holding too much land. So you can either hand out land to get less embezzling, or conquer more if you already hit the maximum penalty of 65% money lost.
myself 说:
setting Campaign AI: hard medium easy - 8 10 12 center points till TI (Tax Inefficiency) ticks in. 2 points for a town, 1 for a castle or location.
setting Loss penalty: hard medium easy - 4 3 2 (% of total income from taxes)
So you can keep e.g four towns tax free at hardest difficulty - or 8 castles/villages - or the typical Royal Household - 1 village, 1 castle, 1 village, 2 towns. Any center point above it is taxed with 4% at hard campaign difficulty.
The maximim tax is 65% - means you can´t go under 35% total income!