Minecraft wiki entry for Traps, associated text: Dig a hole (2×2 works best) at least 30 blocks deep, the deeper the better. At the bottom place a block of lapis lazuli, a block of blue wool or a block of blue stained glass. Add a false corridor at the bottom to make it look like it goes somewhere. When an unsuspecting player comes across the hole, they may think that there is water at the bottom, jump down and die. Experienced players are less likely to fall for this particular trap but it generally works quite well. You can also place real water instead of blocks if you're wearing frost walker boots, just go down there, hide in the fake secret passage and sneak to hide nametag. Use F5 to see if a player is coming. If someone falls down, quickly move to freeze the water.