Treat it like you would your own house
if managing yourself yearly inspection :
- furnace/boiler - clean out burners (do in Fall to make sure heat is on in winter)
- clean dryer vents
- caulk bathtubs
- change out thermostat/CO2 detector batteries
- clean out gutters in Fall
- while on the roof looking at gutters, take a look at roof condition - fix early
- vacuum and clean utility room near any furnaces and water heaters (keeps dirt/dust out of systems, can extend life)
- rinse water heater screens (can fill with dust and won't stay lit)
- drain water heaters yearly - prevents sediment buildup and will extend life
- change furnace filters (more often than yearly)
- if in cold environment, turn water supply to exterior off before winter
- take a look under sinks to check for any slow leak
This shouldn't take much longer than an hour or so per unit per year unless you find something unexpected, and if you do find something then good job catching it early. Alternatively, if you have a property manager, make sure they're doing this yearly to identify anything that might be missed. You still need to see for yourself to ensure nothing is missed.