Fuel filters-as needed, or whenever I just feel like changing them. I've done the fuel filters in my '83 twice in 6 years, but I only drove 18k miles in that time. My '77 picked up a fuel contamination issue while I was away on deployment once, and I must have changed the fuel filters on that thing four times or more in 24,000 miles.

Air filters I just inspect occasionally and change when they get looking bad. I used to work at Firestone on Howell Mill in Atlanta and I noticed LOTS of dirty air filters compared to the shop in Mississippi where I worked previously.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.