Inform your landlord if any part of the property is in poor condition. This will prevent you from having to pay for something that was already damaged when you first moved in.
Conduct a second walk-through about 2 weeks after living in the rental unit. This is important because you will discover some things only after living in the unit.
Document all defects, and get agreements for repairs in writing.
Consider taking photos as proof of any damages (use a camera that automatically imprints the date on each photo, if possible). Save the photos for when you move out in case you need to withhold costs from your security deposit.
When repairs are needed, document them in writing and have the property manager or owner sign to that effect. Read about landlord responsibilities for repairs.