Organize a meetup! I gave a 45 minute talk in SF last week, and I felt it provided a good environment for creating and honing teaching skills.
It was the hard deadline that got me to actually create a message, a slide deck, and hammer down a presentation. Without such deadlines, it never felt "real" to me, so I had a hard time improving.
The meetup doesn't have to be on an advanced topic, either. There are plenty of intro-to-programming meetups which would be happy to have a guest speaker. Granted, the audience can vary wildly since it's public, but all in all I recommend it.
