I start by showing them an interesting picture, and I say, "Tell me a story about this." Immediate reactions are generally, "I can't!" or, "I don't know."
I reply, "Sure you can. It's not MY story. It will be YOUR story. You get to make it up. Pretend. Use your imagination."
Amazingly, after I ask them the five "W" questions: who, what, why, where, when, the three year olds can stay on topic for three related sentences. If they get stuck, I ask, "Then what happened? Tell me more?"
The four and five year old pre-kindergarteners add rich details, learn to describe and create dialogue. This story project was done by a little boy who will be four next month. The kids think they are just twisting tissue paper, but actually they are strengthening hand and finger muscles that will make them good printers. By the end of the year I can see the future writers in my class just by looking in their story folders.
This fall tree was made by cutting off the bottom of a lunch bag and twisting half way up, then cutting the top into 1/2 inch strips and twisting each. Scrunch up 3 inch squares of tissue paper and glue on the branches. Vocabulary enrichment: branches, trunk... and so much more.