Most newer cars and truck use platinum spark plugs which dont need to be replaced but every 100k miles. The serpentine belt shold be checked for wear every 15k or so. Replacing the spark plug wires is good idea after every 50k, along with the fuel filter. Transmission fluid should be changed every 30-40k miles depending on how hard you drive it. And of course you want to check the axle fluid every 10k or so to make sure it isnt low, and change it when you do the trans fluid.
Air filter change every 15k miles or so. PCV valve every 30k.
84 Ranger XLT, 2.8, Auto, 2wd
02 Lincoln LS V8, 5 Speed auto, Leather, Chrome 17"s