What do you wish you knew starting out?

[Warren West]

I just won the bid on a duplex that I plan to househack as an owner occupied.  I'm working on the inspection and rest of the closing pieces at this time.

As I get closer to closing I need to start thinking about renting out either the top or bottom unit.  As this is my first rental property I would love to hear from more experienced people to hear about the errors you initially made, or just things you had wished you'd done differently, so I can learn from you and start off on my best foot.