One of the biggies is the dog needs to already know what is expected, be trained to expected behavior. The ecollar is when they know but choose to ignore the command, like a simple 'come'.
Dogtra is my brand of choice. I also think the 'page' feature is very important. The gentle reminder with some vibration is usually all it takes, besides just wearing the collar.
You can always look over videos on Utube or other sites about use.