Unfortunately, we do judge books by their covers. There are so many wonderful books out there but the one thing that'll make that book stand out to readers is that striking first impression. As an author and designer, I've seen this done wonderfully so many times to the author's benefit, but I've also seen many mistakes that have unfortunately set back both the author and designers who aren't as experienced in the art and marketing behind book cover design.
To help provide solutions to common mistakes I've seen, I will include some examples of book covers done right but I won't include examples of 'bad' book covers because I don't want to artist shame, especially when no one has asked me to critique their work (I'm looking at you 'I fixed so-and-so's artwork without asking if they were okay with me trashing their work' ArtTubers), and also what is and isn't 'bad art' is really up to interpretation.
A lot of these points may apply to only authors or only designers while some will apply to both. Regardless, the purpose of this list is to give authors tools to communicate to designers what they'd like to see in their book covers and to help artists who have little or no experience in cover design ease into this specific area of design.
If you have any further questions, definitely put them in the comments, I'd be happy to answer them.
Not Aiming Your Cover Towards The Book's Target Audience
This is so crucial! (and is the main reason why hiring a professional designer is so important).
As previously mentioned, book covers are key to marketing your book, so it needs to be directed to the book's intended audience. There are two major aspects of the book's target audience that you need to consider.
Genre and subgenres
For example, horror fans will mostly go for a dark, creepy-looking cover, yet fans of gothic horror will be attracted to a certain eeriness and subtle horror that should be reflected in the cover.
This is the cover of my debut gothic horror novella HELENA, designed by the amazing Matthew Revert.
We wouldn't use this type of cover for a cozy romance story for example as it gives all the wrong signs to the point where it wouldn't attract the right audience. A cozy romance reader would likely think they've accidentally stumbled into the horror section or understandably think the book isn't for them based purely on the cover.
The dark colours also suggests dark undertones to the story, at the very least suggesting that it is a horror story.
The gothic font and the Victorian-style border also suggests a gothic and potentially historical setting which would appeal to historical genre fans and gothic fans.
And finally, the picture of a woman and the feminine titular character will also let the audience know that the story is centred around a female character, thus drawing in readers who are looking for a female-centric narrative or voice.
Regardless of if you're an author or designer, I would suggest making a list of traits that the perfect reader of the book may have. This will help keep a clear focus on who the cover should be aimed towards. The traits for Helena for example, traits would include being a fan of horror, gothic horror, supernatural themes, female heroines, Victorian-era history, etc.
Age group
The intended age of your audience is also very important. Normally, this also goes hand in hand with genre since young and middle-grade fiction are classified as their own genres, but it is worth mentioning separately from that as two readers might both love science fiction for example, but an eight-year-old sci-fi fan would require an entirely different book than an adult sci-fi fan, and thus an entirely different cover.
The difference between a middle-grade, young adult and adult fantasy book cover should be drastically different, not only so the parent of a young child doesn't accidentally buy their kid an adult dark fantasy rather than a wholesome middle-grade fantasy but it also gives the reader an idea of what they're getting themselves into (as any good book cover should).
However, this is not always a stern rule. For example, the young adult genre is traditionally geared towards teenagers no more than 18 years old, yet it is still a popular genre with people above that age range. The same could be said with some middle-grade titles.
One such book is CORALINE by Niel Gaiman, which is categorized as a middle-grade due to its young protagonist, coming-of-age themes and writing style, yet it is a book I definitely wouldn't recommend to a very young child but could easily recommend it to anyone over 10. Thus, the designers and the author must make the choice of which direction to take the cover in.
These two covers for CORALINE appeal to very different age groups. The cover on the left would be much more appealing to the adult fans of Coraline due to its dark and creepy imagery while the one on the right would be more effective in drawing middle-grade fans than the previous cover. This is thanks to the different direction of the cover design with the brighter colours and less eerie aesthetic.
Take note that both of these covers present similar aspects of the story (Coraline herself, a creepy setting, etc.), but the design choices made still greatly affect the impression a potential reader will get from the cover. Hence, if your book is clearly gaged to a singular age group (with a little wiggle room), it is crucial that you take this into account when thinking about the direction of your cover.
Summary
TLDR: One of the best ways to create the best book cover for the story is to single out the intended audience. In addition to what I've previously mentioned, a good way to gather inspiration by finding other books that are similar to yours or match the vibe you're trying to create and evaluate what makes the cover of those books so effective.
Also, if you are the author communicating with the designer, be sure to send such examples of covers and artwork you like to them. They probably have already done their research into your book genre and what direction they should go in design so having an idea of your personal taste as well means they can meet the perfect medium of a cover you like and a cover that'll attract your readers.
Not Checking The License for Your Stock Photos/Fonts
This is more so for the designers but holy mother of Satan, please make sure if you are using stock images that you've either purchased the rights to use or are under a 'free to use' license. No one likes getting sued for using materials that aren't theirs.
Not Hiring a Professional Designer/Artist
I promise you I'm not biased when I say this.
Unless you are a trained/experienced artist or designer, it's probably best if you do not attempt to design the cover yourself. Although it is very tempting to give photoshop a try as book covers can be expensive but like editing your manuscript, book covers are a worthy investment that directly affects the outcome of your book sales and success. You've already put way too much time and effort into writing and editing your work, it would be a shame if no one picked it up because of the cover.
Also, when your initial main selling point is the book cover, especially when marketing on Bookstagram and BookTok, you're going to want something that'll make you stand out and grab the reader's attention out of all the other books readers see every day. A professional is someone who is going to help you achieve that.
Overcrowding the Front Cover
99% of the time, less is more.
As an author, I understand the desperate urge to fill your book cover with 1,000 references to the plot, characters, symbolism, small hints about the meaning behind the story, etc. Even now, I still struggle with it. However, at the end of the day, trying to cram all of that into a small space is just going to look messy and overwhelming.
For example, here is a concept sketch of my book WHEN WE ENTERED THAT HOUSE compared to the final cover which I was able to design myself.
Even after I reduced the 'house' to just the signature red door, I was still originally going to have the main characters Zoe and Elle standing by it. I'm glad I dialled it back even further because I think it created so much more mystery to the already eerie title and cover design. Plus, then the vibrant red door sticking out of the dark forest became the focus of this mystery.
LOOKING FOR A COVER DESIGNER, ILLUSTRATOR OR ARTIST FOR YOUR UPCOMING PUBLICATION??
I can help! I've worked with a wide range of publications and authors including Off Limits Press, Cemetery Gates Press, Ghost Orchid Press and more. Here is my portfolio if you'd like to have a look <3