Kathy Sierra has a great post on Ten Tips for New Trainers/Teachers. Including that it is almost always far more important that your learners nail fewer subjects than be "exposed" to a wider range of subjects. This is one of my personal favorites as I tend to always want to cram too much information into a presentation. Sure, like most it starts with a nice simple design, a few slides and a few words and we'll let the questions fill in to round it out. Then, mid-way through the preperation it hits you, maybe there won't be any questions. I'd better prepare a few backup slides you say. And then the backups become a part of the show and so it goes.

Read more of Kathy's tips. Thanks to Matt Raible for the link.