When you own the property and live in it.
Some people do this really well. Most people don't do it very well atall. Clear boundaries are REALLY important. Late rent needs sorting the day after without fail (you are not their bank).
It can be a good idea to assume responsibility for cleaning communal areas like living room and stairs and bathroom for yourself or a cleaner employed by you. In a very modest and self-effacing way this clearly 'marks' you as the 'chief' but also sends a welcome message to your tenants that you acknowledge some responsibilities in return for their money and that they are not just there 'to pay your mortgage.'
It's good to allot cupboards and shelves in the kitchen, bathroom and living room for your tenants: Even if they don't use them, they should still be left empty, even if it upsets the symmetry of your living room. The reason is that the home is not just the bedroom: humans are much more flexible than animals about territory, but small spaces like cupboards are surprisingly important.