I'll never forget teaching my first EMS class. I felt really wooden standing behind the podium. I knew my material and had all of my notes but still it was a bit unnerving. We took a break every hour for the smokers and to stretch our legs, go potty and such. In the ambulance bay my words just flowed, as soon as I stepped back behind that podium, I once again changed into the "instructor" role.
I learned quickly to get out from behind the podium and walk around, amoung them as I taught. Also it is a fact that people remember a lot more of what they see than what they hear. Visual aids help a lot. They didn't have laptops back then and I spent hours on Microsoft Paint making overhead slides for the old projector. The store should have a lot of the equipment that they will need, I'd arrange it so that they had a lot to look at, it will help them absorb the subject more. Pictures help a lot also.