Minecraft the best way to make a mob trap?

(Ignore the weird account name it was made when I was 9)

So I'm looking to get mob drop fast and easy anyone know a way to make a good mob farm? I've seen the videos on youtube but I normally don't do well when copying from a vid. Any ways whould be appreciated.

I just make a high, dark tower where mobs can spawn about 20 blocks above ground. Then, every 3 minutes, water will be dispensed and it will push the mobs down the tower and fall to their death. I put hoppers down there so I can automate picking up the loot and put them in the chest.