Buy properties with more and more units.- Can also try to do seller financing, but much harder to find.

The early portion of my career was buying turnkey rentals, like the one you described. 

I am not sure if I would make the same decision today.However, if you think you can purchase real estate and have a SIGNIFICANT delta as an investment, I would not cash out the 401k now to buy real estate. 

Quote from @Alex Spivey: I want to start renting as soon as I can so does anyone have adviceYou want to find a place to rent and occupy, or you want to buy an investment that you can rent to others?

Turnkey, buy-and-holds, flips, or something else?

Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

I would recommend buying new construction or turnkey properties.

This acronym stands for Buy, Rehab, Rent, Refinance, and Repeat.

Joint ventures entail utilizing your own money to buy properties with others.

Then, if you can trend over time you'll want to see where the "path of progress" is going/moving and attempt to buy in that path of progress to gain some appreciation in the future.