You have to know the local agriculture at the time of year that you
are flying, and then qualify the off field landing options.

A farmer's field could mean sod, hay, cultivated crop, livestock, plant nursery, orchard, tree farm, and lots of other stuff. Each type of crop has a different set of steps for farming. Depending on what the farmer and mother nature have been up to recently, it might be landable or to be avoided.

Choosing requires time for a careful look and some sense of what farmers do in your area in the current season. No fixed rules, but the above list is somewhat ordered from most to least likely landable. Most try to avoid getting to a situation where they have to land with 'the cows' and below on the list.

A known airport might be first on the list, but an unknown one might be a ways down, especially if it hasn't been used in a while.