Using it how? Fuel system, crank case before an oil change, top end cleaning such as introducing through your brake booster? What is your goal?
Using the SeaFoam to clean the top end will require you to use it either in the fuel tank at fill up or thru the brake booster or vacuum line feeding the manifold.
Putting the SeaFoam in the oil before the oil change is cleaning the bottom end.
It depends on your reasoning of use to where you put the SeaFoam.
A smoke screen out the tail pipes will only happen when you use it directly into the manifold, ie: brake booster or vacuum line. And that is a good thing, it is doing what it is supposed to do, cleaning deposit build-up in the intake, valves.
SeaFoam is meant to only clean up the carbon build up through the top end, and oil build up deposits in the bottom end when used in the oil.
I usually add a can of SeaFoam every 4 or 5 fill-ups. It does all good and nothing bad. It is a great investment as a regular fuel additive. Only downfall to this method I use is if there is deposits in the fuel system it could clog up injectors or disturb the injector spray pattern. Other than that, it is a safe and clean method to help keep the upper end clean as possible. I virtually swear by the product as I have been using it for years and on all kinds of makes and models.