Step 1, learn to elide almost everything except what you're actually teaching. This is surprisingly harder than it sounds and often involves saying things that are technically untrue.

Step 2, teach the things required to do tasks.

For a child, you should focus on things that they can understand the output of. Sound, animations, pictures. Turtle/logo is a fantastic platform in this regard.

For, well, everyone, you need to ensure that what you're teaching is what they're interested in. If they're not excited about moving a cursor around a canvas, then they won't learn anything.

You'll know you're teaching correctly when they start doing things on their own that you didn't expect.

Sean