* Practise unusual voices. Start with a tiny high voice and a gruff deep voice.
* Use movement as well. Storytelling is not about sitting quietly with a book. Get up, walk around, get down on your hands and knees. If you don't feel comfortable doing this, work on using facial expressions to get across the power of a story.
lRead the story in advance as many times as you can (even once is better than nothing). Look out for places where children can participate (repeat phrases, do actions, jump up and turn around, make noises). Even older children who are trying to act cool enjoy the more gross, disgusting noises and references in "Aunt Mabel's Table", for example.