When you are renting the apartment on a month-to-month basis, the landlord is required to give 30 days written notice on the day rent is due if he or she intends to raise the rent or terminate the rental agreement the following month.
If you are renting under a term lease (for example, a one year lease), the landlord may not raise the rent during the term of the lease and must give proper written notice if he or she wants to raise the rent starting the first month after the lease ends. (§ 76-1437)