On the “Writers Helping Writers” FB group, Susan Uttendorfsky (of www.adirondackediting.com) offers the following excellent advice:
Thinking about working with a cover designer?
The old saying, “Don’t judge a book by its cover,” just isn’t true, it seems! A lot of people do review a cover first before looking at the back-cover blurb or the reviews. If you decide to hire a cover artist or designer, there are some things you should think about (and ask) beforehand:
• Approaching a designer with a vague idea like “a girl in a swing” will end up costing you a lot of money in revisions if you already have a certain idea in mind. Being explicitly detailed will work out better: “A blonde, long-haired woman, 35yo, in an old-fashioned rope swing attached to an elm tree. She wears a white, billowy dress that streams out behind her as she reaches the apex. It’s early autumn and she’s alone. There’s fog in the background.”
• Your title needs to be set in stone. Making changes/tweaks after the first design draft is complete may affect more than you realize!
• Be sure you understand all of the charges and the process. How many revisions are included in the original price? What is included, and what will cost extra?
• While you have an idea of what your cover *should* look like, you’re paying for the designer’s professional expertise. So if you don’t have any preconceived/prearranged ideas, then let the designer have free rein! They’ll be able to show you their best ideas.
If you’ve hired a cover designer, how did things work out for you? What would you do differently next time?
In reply, I wrote:
“If you give the designer free rein, it might be a good idea to ask for what are called “comp sketches”, which are rough layouts where the designer can show you several potential ideas, quickly drawn. You can either work the cost for the comp sketches into your overall price, or pay for them separately. Even if you have one idea that you’ve fixed upon and agreed on with the artist, it’s good insurance to see a comp sketch of that as well before the artist proceeds with the finished piece. Personally, as a commercial artist myself I would ask for a colour comp (where the colours are roughed in as well).
“For example, here’s the advanced colour comp sketch I created for the (ultimately unused) cover of my own novel. It’s clearly not finished, but there’s enough there that you can get a good feeling for how the final will likely turn out.”
Below is the rough comp sketch I created for an unused cover for “The Codex of Desire”:

And the colour comp stage you might typically see after you’d approved the black and white rough comp sketch:

Once this type of colour comp is approved, the artist generally moves on to the final painting phase, since this gives a pretty good idea of what the cover will ultimately look like. 🙂