Take at least 7 percent of the rent money and put it aside for maintenance. Take another 10 percent for those times the house is not rented so you can pay the mortgage.
Hopefully, any money you put into maintenance and costs associated with the mortgage is tax deductible as a business expense where you live.
Remember there is normal wear and tear that you will be responsible for fixing. And of course there is the time you spend as a landlord on top of your day job. Hope you don't get a tenant that decides not to pay rent. Here in California, it can take 3 to 6 months to remove a non-paying tenant.
It's like mass production, a small amount from a large number of rental properties adds up to a decent wage. It will still take a lot of your personal time, but should be worth it in the long run.