Try and find someone who can help you do a tune up. The dealership or mechanics shop will charge you an arm and a leg. I dont know what your knowledge base is on vehicles but doing it with someone who knows about the truck is great first hand knowledge to start doing everything on your own. Maybe I am just spoiled but I have a great support group who are willing to help and even show me how to do things.
If you really dont know anyone or dont want to jump in and try things I would take it to a dealership. I have a hard time trusting anyone working on my trucks especially a mechanic from a shady shop.
Like said above additional to your oil, plugs/wires you can change fuel filter, air filter should be changed, check trans fluid/diff fluid, belts and you can also look into Pm3.
Inspect your brakes (especially for leaks around wheel cylinders) ball joints/tie rods. Pretty much everything can be checked and should really be checked all the time not just at tune up time.
'99 Ranger XLT
3.0L Flex Fuel 2wd
Stock Ranger on Kelly Safari tires on stock wheels.
7.5 3.73's w/ L/S
3" Summit Body Lift
3" Spindle Lift
2" Rear Blocks
33" Mastercraft Courser CT's fitted on 17" IONS
8.8 4.56's w/ L/S
Coming soon: Exhaust