Having enterprises in every town and having as many town fiefs as possible helps with money. If you combine this income with prisoners and item drops in war you can usually stay in the green financially.

fief upgrades can help a bit but depending on which one you own it might not be worth it.

dont keep villages as fiefs, go for towns if possible. you can ask friendly lords to follow you into battle by talking to them and if you succeed in taking the town you can then ask for it and talk to them about supporting you. for a quick boost in money look for towns with a lot of prisoners then transfer them all to you and sell them in the taverns.

after owning a castle or a town set it to not transfer money so none of it is lost during transfer and you can pick it up as you need it. this also pays for the soldiers stationed there fully or partly.

you can also start buying land in towns but you need to manually gather the money each month. make sure to buy land not prepare it as you can prepare too much for a town of that size and lose money easily. theres a topic/comment in the perisno forum explaining how much land each town should have based on its population. the dwarf towns can have a lot of land and earns an ok profit.

when buying enterprises in towns check what the surrounding villages produce so it will be a bit cheaper. or just buy dyes and weavers everywhere as thats normally a pretty good way to earn but costs a lot to set up.

might also drop profits as you add more. not 100% if they ever got that working but i remember someone talking about it.

- Buy land in towns that you can go & collect the income every couple of weeks.
(It's expensive to buy, but pays off in the late game big time!)

- Trade prisoners! Trading prisoners is very profitable!

- Purchase buildings in Towns, stick to only the bottom 4-5 buildings, you shouldn't really buy something that won't generate you more than 2,000 per week.

- Tournaments! If you bet on yourself & win tournaments you can easily make 12k - 13k!

- Sell loot (weapons & armour) you collect from defeated enemies.

- Loot villages your faction is at war with! It is very profitable looting villages & be sure to lead the cattle to towns, then slaughter and sell the meat. Looted villagers with cattle can easily generate you 12k-15k

- Complete Guild missions, granted not a lot of money for doing these, but hey, every little counts!