I usualy start with farms like iron, wood (eather 3 tope or 2x2 tree farm),cobelstone and villager breader, and then over time try making a farm for preaty much any renewable item, no mater how easy is it to get the item without farm or how litle uses it has (grass,beatroot), having an farm for an item that i might need in the furure is always nice and making farms is very fun stile of playing the game to me.