Get a Woodland Explorer Map from a Cartographer Villager
Trade with a Cartographer until the map appears
Follow the map marker to the mansion location
Use the map to travel through forests and across terrain
Enable coordinates to help track your route
Bring food, weapons, armor, and blocks before going
Use a boat if the mansion is across water
Search dark oak forests, since mansions generate there
Use the /locate structure woodland_mansion command in Creative or with cheats enabled
Fly in Spectator or Creative mode to spot it quickly