One of the finest exploits in the game is to put archers on the front line and DON'T have them retreat. No matter what difficulty you are on, the enemy will not attack (unless you hit fast forward and the line accidentally hits you in one of their false charges). This is especially true if the enemy has archers themselves as that causes them to sit back and wait for the archers to finish. If you have more archers/crossbowmen/javelin throwers, wipe out 90% of their long ranged units. As you archers die, their arrows are transferred to the still living company. You can sit back for 10 minutes cutting down the enemy and since it takes so many arrows to take someone down, then siege equipment (like ballistas) are more effective the longer they can shoot (plus the 20 people in a siege company are hard to hit and have decent armor). All you need to do is spread you army as thin as possible to reduce arrow causalities and wait them out. Since the enemy is less likely to spread their lines, they will receive MASSIVE causalities from a straight on ballista shot. Then rush then while collapsing your lines into a tight formation to get a surround on them. If the enemy has siege equipment, use you cavalry to wipe them out (any engagement will cause the enemy to charge towards you lines and break the stalemate). Keep your general back and focus on the company that contains their general (especially if it's just a captain). This will at least make his company weak to a later assault charge. If you work like the mongols, then you can use all horse mounted ranged units and you can combine the circle and shoot and retreat when pushed options making you unable to get charged while dealing massive causalities.
Evil Pays Better: Instead of occupying a settlement with a minimum of fuss, you can choose to sack it, looting and tearing up the place while eliminating part of the troublesome population. In Medieval II, this kills off lots of people, gives you the same amount of money as occupation, brings the settlements public order up a lot due to fear and a massive fall in squalor, and greatly reduces the value of the city. Some Middle-eastern factions can enslave the populace instead, which is functionally the same thing. It really depends on where you're attacking. If you're playing, say, Spain or England and are on a Crusade to Jerusalem with one or two armies, it might make more sense to invade cities along the way, massacre the populace, sack the town, destroy every structure in the city for money, and then keep on going without leaving any troops to garrison. The city will rebel and go into anarchy, but that's fine, because you're not there to take territory, you're there to pillage and plunder and destroy the faction you're crusading against. Even better, if you release prisoners or successfully ransom them off, you can get chivalry points. Send in you priests to pre-convert the population and then sack the town. You get more money, less squalor, less disorder, and BONUSES for lack of religious diversity and having a "chivalrous" run the place while killing thousands of civilians and sparinga few dozen soldiers.
Good Feels Good/Good Pays Better: Yes, it does. In addition, it can pay good too and negate potentially evil actions like sacking. Having chivalrous general run a city increases population growth and happiness. The more happy your city is, the more taxes you can charge it as well as getting more people to pay taxes. If you have an architect and are quick in building walls as well as public building that take away squalor and unrest, you will increase population growth and decrease disorder even more. If you ally with every faction and start trading and make markets and ports, there will come a point where certain items that merchants can sell will be worth TEN TIMES what they used to be and your income from trade and taxes will be so high that you can always have a building with positive modifiers being constructed in EVERY ONE of your cities. Keep up you relationships with foreign powers while converting your population and making garrison units (which increases happiness in castles) and you will become rich. Then convert all but your most advanced castles into cities (you only need so many castles building your advanced units and cities can be taxed unlike castles) and get even more money. You can lower taxes to increase morale and increase population growth so you can get new walls earlier and more people to tax later. Center your capital somewhere in the middle of you kingdom to make sure every one of you cities feels important (distance to capital can cause negative effects if too far away and positive effects if close). Have a family member (non-greedy ones) run you cities and let them deal with rebels to keep them happy. Build race tracks, inns, town watch garrisons, mayors' houses, city halls, farms, markets, ROADS, churches, walls, chapter houses, etc. and the people will be eating out of you hands while you sack cities for money and gain morale points for conquests and buying out other merchants. The money will never stop flowing.