Before you jump into being a landlord, you should identify who you want for tenants. Families? Students? This will help you identify areas and properties that are appropriate for your target market.
I decided I wanted to rent to families who wanted a detached single family home in a good school district. Highly rated schools are a big draw. Families need space, so I looked at homes with four bedrooms. A nice yard is also desirable, as is proximity to workplaces, transportation, restaurants, shopping, and medical care.
I evaluated each house as someplace my family would live. If I would live there, it passed the test. If not, I thought really hard about why this would make sense to purchase.
Getting started I worried that being a landlord is something I might not like doing, so I also evaluated the potential exit strategy for each house.