Taxes.
As a ruler or leader, you collect taxes from the people you rule/lead. Some of those will need to be paid up to your liege, but you get to keep whatever is left over.
Also: rent.
The mayor of a town is generally the biggest landowner in town. Land parcels are much larger than the buildings we've seen so far. There's plenty of space for you to place numerous buildings on a single plot of land. If you build residences, shops, workshops, and other useful structures, you can lease them out and make some money.
Or you could make the workshops free to use (public workspaces) to encourage more players to come to your town since they get a workspace they can use for free while building up their skill until they can build their own workshop. This leads to a larger town, and thus more tax revenue.