Without a starting photo, the prompt defines both appearance and movement. Begin with one clear episode. A short clip is easier to direct when its action has a beginning, development and visible ending.
Not every model requires English. Start with clear wording in your preferred language; compare a reformulation if it is misunderstood.
It may contain competing actions and conflicting directions. Keep what can actually happen within the clip.
Text may not preserve an exact face. Prepare a character image and use a reference-capable model.