My approach was to buy into a neighborhood in Dayton, Ohio that had a lot of vacancies and low rents, but first researched the area and found one that the city planners had in their sites set for rejuvenation. The city had big money for demolitions and I worked closely with them (and bought two houses off of them) to investigate the vacancies. I ended up buying everything I could along a particular street that would be when fixed up and once was very beautiful. The houses were built in the 1950s and 1960s with far superior construction standards than are common today. I made these places really nice by polishing, painting, repairs, and landscaping. I then charged well above market rates which priced out section 8 and others. Its really amazing how much the north riverdale area has improved. Along this 6 block street, Kathleen ave, the city has torn down five houses and I have rehabbed and rent out three more. The rents in the area are up 40 percent over the last five years and a lot of other investors are now buying! I am not interested in selling, but if I were, the returns would go from over 25% to something astronomical.
Really key to success is
1 - make them distinguished (beautiful retro look in my case)
2 - tenant screening - get people with jobs who can afford the rent and actually want to buy the place
3 - choose your neighborhood wisely.
4 - buy houses in close proximity so you can keep an eye on them, but also so you can improve the neighborhood over time by your own work!
5 - good luck! you may be needing it