whats really fun is to make a long 2 thick hallway. make the floor trap doors then dig under the trap doors about 2 blocks down. put lava in the hole then at the end of the hall you have pressure plates or a lever hook all the trap doors up to the lever with redstone then you have a nice trap for any mob trying to follow you

I don't know if it'll work, but you could hook one up to some redstone. When a player tries to open it, it activates TNT. I probably won't work... Just a suggestion though...

what one of my buddy in my server did is made a lava pi with trap door over it then connected the doors with Redstone to a switch back in his base a bit, this trap is over the only entrance so it works great for pvp and things at night, ya u dont get the drops but what u could do is dig a big one with no lava and traps things and night then open it up in the morning to let then things burn and stuff, but if you get a creeper or spider just use your bow to kill it fast and safely :)

Well what you need to do is make a big hole and then climb out of it.Next you put the trap door at the top of the trap.Then you put a wood or stone pressure plate next to it and there you have a trap