Find or build a dark enclosed spawning area
Spawn-proof all nearby caves, tunnels, and surfaces
Make the floor solid blocks with no light sources
Use trapdoors, slabs, or carpets to control mob spawning if needed
Keep the area at light level 0 for hostile mob spawning
Build the spawning platform high enough or isolated enough to reduce other mob spawns
Use cats to scare creepers into a drop chute
Place water channels to move creepers toward the collection point
Add a drop shaft to damage creepers before collection
Use hoppers or hopper minecarts at the bottom to collect drops
AFK at the correct distance so creepers can spawn but stay active
Replace or light up nearby spawnable areas to improve creeper rates
Use a mob farm design optimized for creepers only if you want higher efficiency