[notmytarga]

Cleaning the outdoor coils is a garden hose job +/- after spraying a special/not-special cleaner on them. This really helps with efficiency if the unit has been neglected (dog hair clogged one bad on a past house I bought)
The things that the HVAC checkup guys do that are usually NOT easily DIY are checking the refrigerant pressures, checking the burners for carbon monoxide risk, checking the indoor evaporator coil fins, generally using equipment and crawling into the attic.
I have not had my replaced 4 year-old system checked because I keep an eye on things, clean the condenser coils and change the high efficiency filters on both the upstairs and downstairs units once a year. I went so far as weighing the MERV-10 filters before and after a year of use. These slide into a box on the intake side of the attic units. 90 GRAMS of stuff collected. Not much it seems. But the filters protect the furnace and evaporator fins from getting obstruction over time.

Do you know that smell that you get time the first time the heater fires up for the season? That is dust (skin cells mostly!) being burned off the furnace burners. I haven't had that smell since I started using filters that are better than the "Change every month type" Allergies seem better too. If the furnace is collecting this dust then the evaporator coils are too, probably more so. And it doesn't get burned off - maybe washed off a bit by the condensation. Use the better filters.