If it's not already on a Property Management System (PMS) then put it on a system. Implement Tenant Protection Plan (TPP), increase rates if it's below market, implement late fees, and add outdoor parking if there's extra land. These are the business side. Physically, look at adding electronic gates with keypad, improve landscaping, new signage, paint buildings if needed, install security cameras, improve lighting, and etc. Out of these, what can wait might be adding parking, painting, gates until you have the money to do so...or you might not really need to do them depending on cost and market.