You need to back up a tad to the basics - is everything else all right? Is this a daily driver that just stopped working yesterday with no notice? Look to ignition. Is this an engine w/ 500,000 miles on it that's been on blocks for 10 years that you're just starting a restoration project on? Is there spark? Is there oil in the radiator? Has it smoked like a forest fire for the last 25000 miles? Rings have had it.Has it only smoked after deceleration then clears up? Could just be valve guides. Oil on plugs can be only a few things, but a little more info would shorten the list even more.
Dave