Mount & Blade: Warband

A great way early game to make money is by winning tournaments. Betting 100 denars on yourself each round should have you come out with 7800 denars by winning the whole thing. This is great money to start the game out with to gear your character up.

I find a more consistent way to make money is to by get a fief, be it a town (preferable), castle or village. You earn money each week from the rent and tariffs from your fiefs. You can increase your weekly earnings by increasing your relation with the town/village by completing quests or going to a tavern and buying everyone a drink. When owning a castle or town increasing the wealth of the surrounding villages will end up with an increased wealth of your town by bringing in wealthier farmers.

Selling prisoners to a slave trader in city taverns in also profitable; take the highest tier troop after defeating a war party to sell. You can get prisoners by knocking enemies unconscious by using blunt weapons. Sarranid mamlukes or Rhodok sergeants are good for this.

Lastly, go to each city and purchase a weavery and dyeworks enterprise from a guildmaster. The weavery and dyeworks is almost always the most profitable choice, netting anywhere from 450-800 denars a week. In order to do this you need to find the guildmaster by walking around the town and purchasing it for 10,000 denars while being in good relation with the city's owner (no negative relation). Take note: while at war with an enemy occupied city you won't get money from your enterprises.