All of those conditions are more or less responsible for the overall shape of your AC condenser and its need for maintenance. If the unit hasn’t been inspected by a professional for a few seasons, even if it seems to be performing perfectly well, I would suggest calling an experienced HVAC technician and have him do the job.
Things like checking all electrical connections (disconnect, fuses, breakers, conduit feeding power to the unit), removing debris from the interior of the condenser, and cleaning of the cooling fins should be performed by him.
The cleaning part and dressing of the surrounding area can be easily done by a home owner. Ideally there should be nothing within 3’ from the AC condenser (preferably more directly above it) in any direction to allow for an unobstructed air flow. Before any cleaning attempts you should make sure the power to the unit has been turned off.
I wouldn’t trust the AC disconnect unless you had its interior evaluated by a professional and confirmed that it is wired properly. I’ve seen many of the condensing units having disconnects rewired to bypass the fuses or disconnect mechanism, and if this is the case, moving the handle to OFF position does absolutely nothing, the unit is still powered.
So, after you make sure that the power is OFF you can start cleaning process; wear eye protection, dust mask, and a pair of thick rubber gloves. Leaf blower / leaf sucking attachment can be helpful to remove leafs from the interior but it still might be necessary to unscrew the fan guard. You can also use the blower to remove as much debris (lint, pollen, and dust) from the exterior fins. The same can be done with a soft brush, just be careful not to damage the cooling fins!
After removing the “big stuff” you should spray the coil with a coil cleaner (look for biodegradable brand). Follow the manufacturer’s directions, it usually takes 5 to 10 minutes to dissolve contaminants after which time you can rinse it out using a garden hose. Begin spraying at the coil from the inside (fan area) out, do not use powerful spray nozzles; they can damage the fins.
All of the components of the AC condensing unit are fine with being sprayed with water except for the electrical connection box. There might be some waterproof boxes equipped condensers around but older units are usually semi-waterproof, so avoid spraying water directly into an area where the wiring has been concealed.
Contaminated fan blades need to be cleaned as well; be careful with the edges which can be very sharp.
Let it dry and turn the power back ON…
The interior, “a” coil might be more difficult to service because of the accessibility. Some are easy, some are not, and might require cutting into the duct work or taking apart sections of the furnace / air handler. Power OFF is the first step, careful cleaning of the fins and the condensate tray / drainage tubing is the second.
With the “a” coils positioned above the furnace you have to be very careful not to flood the furnace. It might be worth paying an experienced technician to perform the “a” coil maintenance for you. The most important; change the air filters
on regular basis to minimize the “a” coil’s contamination.