One of the biggest changes in civilization and the one which allowed cities to flourish was the transition from a hunter/gatherer society to one in which there was substantial agriculture. Now only certain people needed to tend to food production and this left the rest of society to pursue other interests including the arts and social reforms like administration and law. While there’s often talk of gardens and small scale agriculture enterprises, even if it’s not shown on the page, one of the biggest decisions I feel an author needs to make in creating a fantasy world is how will food be produced. Will you choose large monoculture/monocrop enterprises (think of today’s corn, wheat, or soybean farms, not to mention others like potatoes or legumes) or will you choose a smaller diversified model of agriculture, one which relies on smaller farms to provide the needs of the populace.
This will have an impact on whether you have larger cities or smaller villages. Will there be shipments of foods or supply lines that need defending? Will the people eat a staple diet with corn or wheat, or will they have a variety of foods? And what is their proximity to trading routes? Are they close enough that they don’t need to worry about growing their own foods?
Large farms which grow only one crop are called monoculture or monocrop farms. These aren’t good for the environment. By rotating crops you’re taking different nutrients from the soil and allowing it to replenish between harvests. Monocrop farms tend to require more fertilizer and more inputs which may not be available in your fantasy world depending on the size and scale of the agricultural enterprises.
Instead, the traditional family homestead with a garden, some crops, and livestock tends to care for itself. For example at the end of the growing season, even now on large farms, cattle are grazed in the corn fields. They pick up any dropped grains of corn and their waste provides a natural fertilizer. When kept confined during other times of the year their waste can be composted to provide additional inputs into the soil. This provides a variety of food for the family and extra which can often be sold at market.
Determining the type of agriculture your fantasy world has will help you establish your society as well as some of the conflicts and characters within it.