Cover design is a whole new area for me. Before I self published, I sold my stories to big publishers. The cover was part of the deal. Sometimes a good part.
First Pitfall — Absent Author
Sometimes not so much. The Author’s input back then generally consisted of doing a précis of the story and describing the characters’ looks. The designer made of that what he/she would. It could be pretty weird. The cover design where the heroine’s only identifiable feature was a bad case of measles is burned into my soul.