A fresh coat of light colored paint on the walls is always recommended. Painting only the trim and the doors will add a lot. Check to see that all doors open and close freely. Oil any squeaky doors. Replace any burned out light bulbs.
Brighter lights enhance many rooms.
Steam clean the carpets if new carpeting is not possible and to help eliminate any pet odors. Wash and wax linolium floors. Repair or replace damaged or missing tiles. Bathrooms should sparkle. Remove soap scum and mildew.