Personally, I would do a standard Seafoam treatment through the intake. I've never had to change plugs afterward.
Also, I try and run Marvel Mystery Oil in a tank of premium fuel every once in a while. Who knows if it works, but I've never had a problem with it.
2006 Chevrolet Cobalt LS - 2.2L Ecotec - 315k
2006 Pontiac Grand Prix - 3800 V6 - 126k
1995 Range Rover 4.0SE - 4.0L V8 - 133k (mothballed with gearbox failure)
"...then I saw that there was a way to Hell, even from the gates of Heaven..."