Start with what you know. Find, ask for previous service records. Then it's basics.
Spark plugs if over 40k mi.
Engine air filter
Cabin filter
Serpentine belt and tensioner
Suction out some power steering fluid for a visual. Do a flush as needed
Transfer case flush
Flush both front and rear diff
Flush brake fluid and check pads and rotor wear
If you don't know when last done; fuel filter

If any of these look like there within service levels move on
Good Luck