I use a more specific method of approach to rental properties that I find is effective across the board, regardless of region.
You always target the following things:
A profit point vs price to purchase
Areas of historical high population.
A price range of 50k-200k.
For me for example, I wont accept a property with a profit margin of less than 20% at the end of the day, all things said and done, its simply not worth my time.
Also, I target a specific profit margin of x per $100 I spend on a property. For example, If I spend 100,000 dollars on a property, I want 20,000 or more in profit at the end of the day.
By following a disciplined guideline such as this, you never buy trash properties that run high costs, you never buy excessively costly properties that the average american cant afford to buy from you if you chose to liquidate, and you maintain a profit margin of your desired end point.
Obviously as well, you can tell that you are more limited in the types of properties that you can buy, and where you can buy for obvious regions, but in higher populated regions, rents are always more expensive simply because of supply and demand.
For instance, in Frederick, MD, my previous abode, I was paying 2800 a month for rent for a house there. Over a 100 years old property, but in a desirable area. The owner was making close to 200% of mortgage on me, but that is the cost to win a house on 5th street.