If your rental activity is not for profit, you would report your rental income as other income on Form 1040. You can deduct your mortgage interest (for your main home or second home), your real estate taxes, and any casualty losses on the appropriate lines of Schedule A, as itemized deductions. You can deduct other rental expenses as other miscellaneous itemized deductions.
If you rent buildings, apartments, or rooms, and provide only the basic services, such as light, heat, and trash collection, you would normally report your rental income and expenses in Part I of Schedule E, Supplemental Income and Loss.
If you provide significant services, such as regular cleaning or maid service, the activity would probably be considered a business, and you would report your rental income and expenses on Schedule C, Profit or Loss from Business, or Schedule C-EZ, Net Profit from Business.
You will need to complete Form 4562, Depreciation and Amortization, if you are claiming depreciation on property placed in service during the year, or on any listed property, such as a vehicle, or if you are claiming expenses for the use of a vehicle.