Before, renting an apartment or unit, if possible, it makes sense to have a chat with other tenants about how they get along with their landlord and whether their experiences have been on the positive side.
Likewise, if the apartment you are going to move into is still occupied, why not have a quick word with the outgoing tenant. Obviously, the best idea would be to chat in private, instead of in the presence of the landlord or his / her employees, who just might listen in. Chatting with other tenants will provide insight into, whether you have a landlord who responds to tenant problems, is conscientious about proper maintenance of the premises, and whether there are issues, such as, noisy tenants, the sound of planes landing and taking off from a nearby airport, or the choo-choo of trains on a rail track close-by, or crime, including frequent car break-ins in the parking lot. These are issues one does not observe when giving an once-over, when out to rent an apartment or unit.
After selecting an apartment or rental unit that a tenant wishes to move into, while legal protections have been extended to tenants, they can vary significantly from state to state, therefore, it would be wise for a tenant to check out, if there is a local tenant organization or union, which can provide information on local laws and policies. If, the selected apartment or unit falls within a jurisdiction with limited protection for residential tenants, it would be best to ensure adequate protection in the rental lease, itself. Include a clause about landlord responsibilities, such as, seeing to it that your unit and common areas are properly maintained. Better safe than sorry!