When you pull a plug you look at the color & condition of the part sticking in the combustion chamber. Pull all the plugs keeping track of which plug came out of which cylinder. A black, dry, sooty appearance indicates a rich condition. Black & wet indicates oil consumption. Medium to light tan is good. White, especially with pitting indicates you're running hot, usually a lean condition.
Keep in mind that if you let the engine idle for several minutes before reading the plugs you'll basically get a snapshot of the condition at idle. It's usually wise to run the engine at highway speed for several minutes, shut it off & check the plugs without letting it idle.
