I've been teaching adult beginning birders for 12 years, in classes of 40 to 60 persons twice a year, and I soon noticed that slides only was becoming boring for the audience.
So I began drawing birds in a simple way, explaining how anyone could make his own field notes no matter how bad his or hers drawing skills. The use of anecdotes you have personally experienced in the field is a great way to get people relaxed, a good laugh is just what is needed every now and then to ease everybody up and get them sharp again on more serious notes.
Try to show passion in every aspect of your teaching, this will be highly appreciated and it will arouse people's enthusiasm to actually go out birdwatching.
Some big, stuffed birds, especially birds of prey and owls, are also good props to have.
If you can, alternate between slides, drawings, anecdotes or whatever, to be sure people's attention is still with you.
Even silly things like urban legends are great, everybody will have an opinion and may participate in an active way.
When introducing bird sounds do not only use a CD player, but don't be afraid to do some impersonations yourself, even if they are dreadful. Try it at home first, you'll be more confident in front of your audience, but remember, a good laugh is often more appreciated than a whole CD of bird calls.
My experience is, that when you are willing to show passion as well as comic relief, people will learn the most.
My two cents, good luck!