If you haven't already, a first step is to designate someone on your staff as your trainer. Once you've done this, send them out for training. Do a program like ABC, several SCAA classes, or even hire an outside trainer to work with a small group (your leads plus trainer?).
This does three things: it tightens up your trainer's fundamental skills, gives your trainer a chance to observe the class being taught, and gives you access to training material to base your in-house program on.
Also consider sending your trainer to the SCAA's Instructor Development Program class - lots of great information there. After that, they can also work as a volunteer assistant instructor at an SCAA event, giving them the opportunity to watch some great lead instructors and gain even more experience.
I personally found the SCAA's intro+hands on espresso class, IDP class, plus Counter Culture's intro class, to be amazing resources when developing my classes. I learned something as a barista and as a trainer, and used their material as the basis for my own stuff.
Sounds like a lot of work, but doing it right is worth it.
Hope that helps.