When you're moving to a new apartment in Seoul...
make sure you ask them how to turn on the hot water.
If you like cold showers then you don't have to worry about this.
If you don't mind just randomly plugging things in or turning knobs on different equipment then you can also disregard that tip.
I was in a bit of luck because I still had the key to the place I was moving out of so there was a happy ending. I felt like a rich man for a few hours, with two apartments within a 10 minute walk.
Which leads to tip #2, which may need to be tip #1: Before you completely move out of a place be sure to ask if anyone will be moving in immediately. If not, keep the key for another day or two until you are settled in the new place...