89 chev siverado ox sensor?

I just bought a 89 silverado 4x4,service soon light comes on at times.The truck runs decent,most of the time,-I plan on doing tune up-plugs,wires,cap etc.I never messed with the ox sensor on my other chevs,service light never came on on them.Gas milage is about 12,using for towing 4 wheeler and trailer deer hunting.My other chevs have gotten better mpg.Am in the right direction about the ox sensor?Thanks