Find a monster spawner in a dungeon, mineshaft, stronghold, or other generated structure
Mine around the spawner carefully
Light up the area to control spawning
Build a dark spawning room around the spawner
Keep the spawner within the required range of the player
Create water channels to move mobs to one spot
Add a drop chute or killing chamber
Place hoppers and chests to collect drops
Use torches or slabs to control unwanted spawns
AFK near the spawner to keep it active