Many people neglect to replace the rear axle fluid, and brake fluid should be changed around 6-7 years old.
Transmission fluid normally lasts for about 15,000 miles, but can last longer with good care and keeping it cooler.
I put a coolant water filter on my RV when it was new. It removes any sand or minerals floating around in the engine water. Napa #Fil4070 and a kit to install it FIL 4019. I only used distilled water too.
Wash the battery terminals.
Not much else that I can think of.
The spark plug change method was well described above. Make sure that you are using a inch torque wrench. Some model years it really mattered not to overtighten the spark plugs. Yours is a later design.
Fred.