You can start by considering the theme of the short stories. For example, if they are horror stories, use dark and spooky colors like black and deep purple. Then, pick an image that represents a key element from one of the stories. It could be a character, a setting, or an object. Also, make sure the title of the book is clearly visible and in a font that matches the overall mood.
To design a book cover for short stories, you need to understand the essence of the stories. Read through them and find common elements. Maybe all the stories are set in a small town. In that case, you could have a picture of a small - town street on the cover. The color scheme should be harmonious and not too busy. For the typography, make it legible and interesting. You can also add some small details like a few lines from one of the stories as a teaser on the cover.