Of course the easiest way to have a tenant to start with is to buy a house that is already rented out. Having experience has a landlord, or as a property manager, is also a plus. One point that confuses many would-be landlords is the income they need to qualify for a loan. The lender does not count the full rental income. Odds are that the apartment will sit empty at times, and will not be producing any income.
Maintenance is also a key expense.
After all, you are responsible for property maintenance, not the renter. You are also responsible for paying the property taxes even when it is not being rented. Of course, there is another way to become a landlord. Rent out the house you currently live in. Once you have a mortgage, the lender doesn't really care who lives there as long as you make the payment on time.