I think a good way to start narrating is to think of yourself as a teacher. Explain what you did why much like you would on dribbble.com
. Help to make everyone smarter by showing your work and the thinking behind it. Aren't celebrity chefs just good narrators? Narration as you label it +Harold Jarche
is also a good step towards external collaboration. Sharing prototypes with beta testers is just another form of narration.