Imagination
The storyteller must have a broad sense of imagination in his/her mind. Knowing that the there are infinite number of possibilities and chances that could happen in life makes the person more flexible to deal with a variety of situations. As a result, the person can improve his/her storytelling techniques because imagination is the source of creativity in stories.
Ability to perform and express emotions
The best storytellers are ones who deliver the action and emotions of the story to the audience using their appearance and body language, even if the story is not very expressive. I believe that this skill include several sub skills such as acting (in a light way), speaking (pronunciation) and making sounds, imitation, and expressing emotions through body language.
Ability to excite and deliver suspense to the audience
This is an essential skill in storytelling. The storyteller must know how to divide the story into subparts, and tell each part according to the action and details in it. Also, a good storyteller is a one that does not give the whole picture of the story, but makes the listener more curious and engaged in the story.
Pacing
Each part of the story has its different way and speed of delivering it. For example, the introduction can be slow and smooth but the climax should be fast because of the rising actions in this part of the story. If the story teller understands the best way to deliver each part of the story, then the listeners will have a better chance of absorbing the story and understanding its meaning.