Looking for tips as I create a new lease agreement

[Evan Rumble]

I am about to move into a house hack (duplex) that I just purchased.  I have one more year until the downstairs tenants lease is up. I would like to create my own lease agreement once this happens, for this property and future investment properties.

What should I make sure to have in my lease agreement that would make my life easier, or protect me as the landlord in the future. Similarly, what could really hurt me if I don't include it in the agreement. ( I would like to hope for the best, but plan for the worst)

ie) pets will require an additional 50 dollars a month in rent; or having an extra charge notated for late rent

Also, if anyone has any horror stories about something not being in their lease agreement. I would love to hear about it.