Try different approaches to maximize engagement. A one-hour lecture is not a good use of synchronous applications. Select your first training course carefully. The first course should be information that's of interest to a large group, but not mission-critical. New users will likely be fascinated by the technology and distracted from the content.
Design breaks in the program.
Keep it human. Make sure the design doesn't imply that you are taking people out of the process. Learning is a social activity, and participants benefit from a personal touch. Build for the content, not the technology. It's tempting to use all the bells and whistles available, but if the media does not support the goal and objectives, it may be superfluous and distracting.