There has been a saying that you might be aware of, which goes like, “Don’t judge a book by its cover.” However, this is not the case when people go out to shop for books. The book cover is the first thing that a customer encounters about your book. While passing through a shelf in a bookshop, if the cover of a book catches the attention of a viewer then they are more likely to buy it. Therefore, it would be naive for a writer not to pay attention to the book cover design [รับออกแบบ ปก หนังสือ, which is the term in Thai] after getting done with the writing. Now, you do not have to design it by yourself, as you might be a writer and there are people out there who are specialized in making such design covers.
Describe the content of your book precisely to the designer:
A designer will not have the time to go through your entire book and decide for themselves what will be the best design for the book cover. You have to tell them what the book is about, actually. Just give them a brief sense of the message or story that your book is suppose to convey. Try to describe things in such a convenient manner so they could think alike you and be able to understand your perspective.
Aim to make a visual image in the head of a designer:
As a writer, it is not your job to come up with a vision for your book cover design. However, if you happen to have a vision to it, describe that to your designer as well. When you are expressing what you feel about the book, have a goal of making the same way as you do about the characters and their tragedy. It is always a good idea to write these things before hand on paper prior reaching to a designer.