In high school, when I was working at Copps Hill Shell in Ridgefield, CT, we were one of the first gas stations in the area to get credit card readers at the pumps for customers to pay at the pump. The learning process for the customers was a bit haphazard, but one of our jobs working there was to introduce the service to customers as they arrived for the first 4-6 weeks of the new readers being in place.
There were a handful of customers who still preferred paying inside of the building, and we didn't discourage customers from paying that way, as it enabled us to capture some sales inside of the convenience store.
Some of the learnings we took out of this were that there is no simple way to train the same way in every situation without having a good system in place. We set up a basic system to follow.
1. Greet the customer with a hello and telling them about our new card readers
2. If the customer said they'd rather pay inside, we'd show them how to do it so they'd become more comfortable the next time around
3. For customers paying cash, we'd also show them how it worked in case they wanted to change their payment method in the future.
Following these procedures got us to know our customers better, educate all customers regardless of whether they'd use the technology or not, and enabled us to be more than just the guys who worked at the gas station.