To win a game of Garrison you will need to master the currencies and different economic tactics in the game. Coins are at the center of the Garrisons economy. You can buy upgrades, buildings, specialists or mercenaries to bolsten your defences. But sometimes, coins are not the best way to get what you need. The resources of the land beyond what is known, are precious and worth a lot to the right buyers. Make sure the Foreman gets whatever resources you have to spare, with him on the trade-ships. Sometimes there will be shortages of a specific resource, which you can take advantage of, and will gain you favorable trade deals.
Another currency in the game is your people. The more villagers you have, the more resources you can collect. To gain more villagers you have to invest in agriculture whenever you can. At the end of each Season, new villagers will come to the Garrison if you have the agriculture to sustain them. They are you most important resource, so keep them safe and keep them working.
Inevitably you will have to spend your resources on your military in order to defend against the invading Enemy Nation. Be wise and plan ahead which resources you need. Sometimes you will not be able to gather the necessary resources to build the troops you need. Make sure to spend some of your hard-earned coins on Iron and Gold in order to train better troops
When the last Invasion occurs, your resources will be nothing worth if you do not survive. So make sure to spend everything you got, and equip your villagers with spears and send them forth into battle!