I have worked in a variety of gyms in the past and their second biggest revenue was personal training. The reason for classes not being a good source of revenue for gyms is that they offer most of them as part of the membership to their members (which I believe it’s a mistake and a loss of a substantial extra revenue for the gyms).
Personal training is our second largest revenue at our gym I’m assuming this will be the case in most facilities.
As for promoting: This start the moment the member walks through the door. Why did members come to your facility? what are they looking to accomplish? Let your promotion be answers/solutions to your members “why”.