The general shape
Financing a rental is ordinary, it is simply stricter. Expect a larger down payment than a primary residence, a higher rate, and a requirement to show reserves after closing.
Requirements vary by program, by unit count, and by how many financed properties you already own. The specifics are worth confirming for your situation rather than assuming a rule of thumb.
How rental income is treated
Projected rent can often help you qualify, usually with a vacancy factor applied and supported by a lease or an appraiser's rent schedule.
For a property you already own, lenders typically look to tax returns. That means a year of aggressive depreciation and repairs can lower the income the lender will credit, even while cash flow is fine.
Underwrite the deal, not just the loan
Model the property with vacancy, maintenance, management, taxes, insurance, and capital reserves. A deal that only works at full occupancy with no repairs is not a deal, it is a hope.