When training employees: What works and what doesn’t

We are a small mom and pop shop with anywhere from 8 to 18 employees given the season and time of year we are in. We are a specialty store and deli and serve light sandwiches and desserts. Although we are a small place we have a lot of items for sale and we pride ourselves on being the experts with regards to the items we sell. From the table linens to the array of cheeses. However, I am trying to figure out when training employees: what works and what doesn’t. I need a better system and process and would love a little bit more guidance and what the best route for education and training might be.