* Have plenty of cash reserves for repairs, turnovers, etc.
* Get a good trusted inspector to do the inspection of the property, check property history.
* Some insurance companies give discounts on your landlord policy premiums if you bundle with your residential and auto policies. Or some give discounts if you pay the premium in full.
* Look for properties in landlord friendly states, that also have low property taxes.
* Focus on newer properties, even though they may cost more, they tend to need less attention in repair.
* If you are getting a loan, put at least 25% down on the loan, and pay for the credit points to get the lowest interest rate possible.
* Increase your rent by about 5% annually (if needed), to keep your profit margins the same, as inflation, insurance, and property taxes tend to rise annually (insurance yes, property taxes sometimes, again depending on the state and city.)
* Find a good reputable property manager, sometimes the mom and pop ones are better than the big corporate ones, as the mom and pops tend to give greater attention to the few houses they manage. Also, make sure they are Johnny on the spot with their communication, as you are flying blind if you are an OOS investor.
* Have separate bank accounts for your personal checking and your rental business to build your cash reserves with direct deposits from your PM on rent collected. Don't touch this money, because you are a HVAC, roof, water heater, septic tank, away from bust.
* Your PM will provide you a 1099 tax form to do your write offs at the end of the year.