If a tenant requests repairs and the landlord or property manager doesn't meet the habitability requirements, a tenant usually has several options, depending on the state. These options include:
A tenant can also sue the landlord for a partial refund of past rent, and in some circumstances can sue for the discomfort, annoyance, and emotional distress caused by the substandard conditions. (To learn more about what tenants can do to get landlords to perform repairs, see Nolo's article Renters' Rights to Minor Repairs.)
Your best bet is to handle repairs as soon as possible (or delegate the repairs to the tenant in exchange for decreased rent). Take care of major problems, such as a plumbing or heating problem, within 24 hours. For minor problems, respond in 48 hours. Always keep tenants informed as to when and how the repairs will be made, and the reasons for any delays.
To learn more about tenants' rights to privacy and repairs, see Every Tenant's Legal Guide, by Janet Portman and Marcia Stewart (Nolo).