Reasons for excessive exhaust smoke?

When does it smoke worst? If it does it after sitting overnight or a day or two it's either bad valve stem seals and or valve guides. The bad seals and or guides allow the oil to drain into the combustion chambers slowly after sitting long periods. Then, when the engine is started, it will smoke. Sometimes badly. It's easily confirmed by removing the valve cover and looking through the valve springs at the seals. They are probably cracked and broken all to hell.