All court papers and other papers you have received from the landlord.
The original lease and renewal leases, if you have them.
Proof of rent payments: rent receipts, canceled checks or copies of money orders.
Records of all apartment and building problems, including problems with heat, hot water, and all other repairs and services, if you have them.
Photographs of all problems in your apartment or building. Label the photograph with the date it was taken and what is pictured.
Copies of letters or other documents you sent to the landlord, superintendent or government agencies (and proof, if you have it, that the letters were mailed and received) regarding problems in the apartment or building.
Receipts for work and materials if you are forced to make repairs yourself after notifying the landlord that repairs are needed.
List of dates on which you talked to the landlord, superintendent or other building staff about problems in the apartment or building.
If your case is scheduled for a hearing or trial, bring all witnesses you want to testify.
Anything else you believe will help your case.