Probably the biggest surprise you will learn today is that a book cover is not designed for the book’s fans. It’s not even meant to please them. A book cover has one and only one purpose: to get a potential reader to stop and look at the book---and, hopefully, pick it up and buy it. It has to attract attention from among hundreds of other books---in much the same way someone might try to draw attention to themselves in a crowd. The cover is shouting, "Hey! Look at me!" And if it fails to get you to look, it's failed as a cover.
To this end, a book cover is really a kind of miniature poster. It has to not only attract attention, it has to get across in the briefest glance something about the book: what kind of book it is, what it might be about, what a central theme might be---whatever seems most likely to inform and intrigue a potential reader.
In fact, it might be best to think of a book cover as packaging, exactly in the same way as the design of a box of cereal, a frozen pizza or a can of peas. The first thing it needs to do is attract attention amid a host of competing products. The next thing it needs to do is tell something about the product itself: is it a can of peas or a can of sauerkraut?
Those are the two things a book cover needs to do: attract the attention of a potential reader then, in a glance, convey some sense of the book's theme, subject or genre. And, if you have done everything right and the gods are with you, the potential reader will pick up the book and look at it.
One way to do this is to try to ferret out one key element from the book, some action or scene that is a set piece, some visual element, symbol or icon that represents the book's theme, idea, premise or character. I think it's important to focus on a single idea. This not only gets the message across instantaneously, it avoids what I call the "kitchen sink school" of book cover design, in which everything important has to be on the cover.
While it is always nice to try to get all the details right, in the end it really doesn’t matter in the slightest whether a heroine’s hair is the right color or the hero has the right number of buttons on his uniform. You will have to have already read the book in order for these things to matter---and if you have done that, then the cover has already served its purpose and any mistakes it may contain are moot.
A fundamental truth is that all the exactingly precise details in the world will go for naught if no one ever picks up the book and reads it. Indeed, a book cover that fails to attract a potential reader has failed as a cover.
As I said, it’s nice to try to get the details right. It’s also a lot of fun to do. But in the final analysis, making the cover do its proper job overrides everything else. A cover that requires a reading of the book in order for it to work is a poor one. It puts the cart before the horse. A cover should intrigue a potential reader, it should not confuse or mystify them. Or worse, completely mislead them. A reader can ask, "I wonder what this is about?" but they shouldn’t be asking, "What the hell?!?"
In short, a cover needs to attract a potential reader, it needs to convey something about the nature of the book and it should make the book seem unique rather than generic.
All that being said, any good book cover illustrator will try to get as many details as accurate as possible. I know I enjoy doing that and most of my illustrator friends do as well. But accuracy must always take second place to effectiveness. If a cover conveys the sense of a book better by depicting two characters together who never actually meet face to face in the story, well, then they will meet on the cover if nowhere else.
But a good cover artist won't play with details just for the sake of doing it, or flatly ignore accuracy when there's no reason to. There will almost always be a purpose. And that purpose, of course, is to create an effective cover. That absolutely always must take precedence.
Every detail of a book cover needs to contribute something to conveying the nature, theme or idea of the book as immediately and clearly as possible. Sometimes, paying attention to descriptions in the book can help this---but sometimes you may have to ignore what the author wrote. Conveying the correct impression of the character's nature or personality is more important than getting specific details right...especially where a literal depiction might be entirely misleading.
A book cover also cannot be designed for the initiated, for those who have already read the book and are familiar with contents. That’s putting the cart before the horse. All too often all you succeed in doing is mystifying---and potentially alienating---new readers. This is why a book cover is not---and should not be---designed for fans. They do not need to be sold on a book they have already purchased and read.
(As an aside, one of the most teeth-gritting critiques an artist can get is "That's not how I imagined my favorite character." We are not mind-readers!)
Authors are generally the worst at this, since it is almost impossible to be wholly objective about one's own work. I remember one author who drove me nuts, fiddling with every minute detail of the appearance of one of his main characters...even though he never actually explicitly described her in the book at all! Again, illustrators are not mind readers!
I don't know how many times I have heard something like this: "You will understand the cover once you have read the book." That is putting the cart before the horse.
Let me give you a perfect example of the kind of backwards thinking that comes from being too intimately involved with a book. The cover of the book was a beautiful image of a rustic stone bridge over a pellucid country stream in a lovely wooded setting. It was the most pastoral thing you could possibly imagine---perfect for, say, a travelogue of rural England. But I knew the book was supposed to be a rousing fantasy adventure, so I asked the author what in the world he was thinking when he designed his cover. "Well," he replied, "one of the main characters is a troll. That’s the bridge he lives under."
Finally---but certainly not least---is to leave room for the title and name of the author. If you are self-publishing and looking for existing art to use, make sure that there is room for the title. At least one third of the cover should not have anything really important in it. An artist doing a cover should allow roughly the same amount of space (professional cover artists will do this). If you are an author who has found an existing image you like, be sure to not fall so much in love the art that you are afraid of covering any of it. Too many book covers wind up with the title crammed into a corner. As important as the graphic may be, the bottom line is that the title is the most important thing. Which means that readability is of utmost importance. Try to choose a typeface that is appropriate to your book, but try to avoid anything too decorative. Avoid fancy effects like textures, beveling, etc.There is no point to having a large title if no one can figure out what it says. Oh...and two different typefaces are more than enough! (There are many examples on this page of the different ways in which type can be handled.)
Probably the bottom line is to always keep in mind Mies van der Rohe's dictum that "Less is more." This especially applies to book covers!
A few covers I've done that illustrate different ways of focusing on a single theme or key element that represents the idea or nature of a book quickly and simply. In some cases, such as River Horses and Dragon Lensman, this was done by picking a key scene or set piece. In others, such as Fahrenheit 451 or Dracula, an image was chosen that symbolizes the book's theme. Likewise Rage, which was about a town torn apart by a senseless murder.
None of these covers depict specific scenes from the books. Instead, their intention was to convey an impression of the nature of the book, or something of what the book is about or what its themes may be. What I tried to do was find one element, image or idea that I thought represented a book and focused on that. Something that would immediately catch the eye of a potential reader and be quickly understood and absorbed.
For these covers, I tried to rely almost entirely on typography.
These covers are more specifically representative of the contents. Each of the elements in the Kessel cover is taken from one of the stories. The Haldeman cover was inspired by a specific scene, which I then made more graphic in order to catch the eye immediately. The cover for The Last Unicorn, however, depicts a scene from the novel very literally. The Undesired Princess is a portrait of the title character.
The Matthews books were tied together both by a similar handling of the type---including the graphic shape behind the title---and a realistic approach to the artwork.
A NOTE ON TECHNIQUE
The covers are realized in a number of different techniques.
River Horses was painted digitally.
Others are a mixture of techniques, often utilising photographic elements. For instance, Future Crime combines hand-painted elements along with photographs. These are almost invariably either photos taken specially for the covers or photos from my own personal collection (I try to never use images from stock image sources). All digital painting and photo manipulation is accomplished with Photoshop.
A cover can be entirely symbolic---not representing anything of the book literally but instead attempting to convey a general sense of theme, subject or idea. A highly graphic approach like these covers for Lois McMaster Bujold's Vorkosigan series can be very eye-catching, as well as establishing the kind of visual unity necessary for a series.