Cover Design

Does anyone else get overwhelmed with the thought of designing a cover? In selling a book, cover design is crucial, but how do you choose a design that is right for your book? Simple or extravagant? Bright or subtle colors? It is difficult to choose a cover design that encapsulates the essence of your book. You want to intrigue the reader without revealing too much. Does anyone have any thoughts on the best way to go about conveying ideas to an artist? Or any suggestions on what types of cover they feel catch the most attention? Also, what are some ways that a cover can subtly and artistically display Christian ideals?