Now there are a few different styles of ignition.
One style has dc right from the battery dumping into the coil and it is stepped up buy the coil. This is your normal car ignition.
One style has a cap that was charged buy the battery, than that cap dumps into the coil, and coil steps up the voltage. This is cdi ignition.
Than to improve on this, you can use one of 2 methods,
One is to run a cap between the ground and positive of the sparkplug. With this method im not entirely sure what is going on but somehow the spark duration is shortened and energy is increased. This results in a slightly delayed and shorter duration but bigger and more powerful spark. Nology hotwires uses this method.
Here is a video about this method
The second method might only work with a cdi box?? It is to use a diode's delayed switching action to switch the paths of current to loop through the coil twice and have the voltage stepped up twice rather than once. result is the same a delayed but more powerful shorter duration spark.
Here is a video showing this style.