Gather building materials: blocks, slabs, trapdoors, water buckets, hoppers, chests, signs, and a killing method such as campfires, magma blocks, or a drop shaft
Find a location far from caves and other spawnable areas, or build high above the ocean or ground
Build a dark spawning platform high in the air or in a sealed area
Make the platform large and flat, with multiple layers if desired
Place trapdoors or slabs to encourage mobs to walk off edges
Add water channels to move mobs toward a central drop or collection point
Create a drop shaft that leads mobs to a kill chamber
Place hoppers at the bottom to collect drops into chests
Add a safe AFK spot above or near the farm so mobs spawn inside the farm
Light up all nearby caves and spawnable areas to improve spawn rates
Ensure the farm is fully dark inside where mobs should spawn
Test the farm at night or while standing in the AFK spot
Collect drops from the chest and adjust the design if mobs are not spawning efficiently