It depends on what the engine is in. If it is from the 1970s it will be a bad distributor cap, spark plug wire or spark plug. If it is more recent, add fuel injectors. More recent yet, remove the distributor cap from the list and add a coil pack instead. Completely modern, remove coil pack and change it to coil on plug. (These are all generalizations, too.)
However, it is always a mistake to replace parts based on probabilities unless the part is either very cheap and easy to replace and/or is due for replacement anyway. It makes sense to replace all the spark plugs for both reasons, but not to replace coils like that. Shotgunning parts drives up the cost of owning a vehicle. In addition, the cause may be not on the list of top suspects. If the problem is a valve is burned, or there is coolant getting into the cylinder from a bad intake manifold gasket or head gasket, it will only get worse if not identified and fixed.