publish an ebook you're going to need a cover.
I like pretty girls and I won't balk at buying a book with a pretty girl on the cover. Obviously, I'm not into Regency Romance novels, but if I were I'd be on the lookout for books with a pretty boy on the cover--some dashing Captain back from the war in a pirate shirt. Maybe holding a sword and looking swashbuckling.
And a girl holding a sword looking swashbuckling is appealing, too. I'm not trying to be a sexist jerk here. I'm just saying that your ebook will have a market and that market will respond to the cover of your book.
Sex sells. If you are gnashing your teeth at the intimation that an attractive female might be reduced to an object of commerce, you might take comfort that attractive males can be so objectified, too. And this is the problem with using sex to sell: you can easily offend unawares or unintentionally. Tread tastefully.
If you are a closet Rembrandt, then all you need do is dash off a pleasing study of your main character doing something interesting--hopefully with a gun or swashbuckling. Sadly, I am not a closet Rembrandt, or Picasso, or anybody else. My art is best pinned on refrigerators with little magnets.
With this in mind I set about finding an artist. Here's what I did and it has worked out quite well for me: I went to Google image search and put in "steampunk" because I was looking to publish a Sherlock Holmes story. I confined the search to deviantart.com. After paging through a few hundred images, I found one I liked. Then I looked at the artist's portfolio and liked what I saw. (I recommend you look for a particular "style" that you find agreeable.)
A few moments later I emailed Joanne Renaud asking if she might do the cover art for The Aristotelian. She would and she quoted a price I found fair. We drew up a simple contract to do the art and get paid. PayPal provided a satisfactory conduit for payment. Joanne and I live in different states, but we were able to make effective use of email, facebook & twitter to convey my vision to her and to get back drafts.
Your publishing project may include a different mix of specialists,
and you should learn to work effectively with each business partner. I recommend that you keep the questions "what" and "how" clear in your mind. You own the "what" and your specialist owns the "how."
I regard Joanne as a business partner and I value her opinions about artsy stuff. I would propose ideas and ask if they worked artistically. I had a devil of a time describing what a Lasanian skycycle looked like and I ended up googling images and saying "like this, but elliptical." I suppose that had we been able to share sketches on the back of a napkin, it might have gone faster.
You should learn to do rough sketches and storyboards. More on that later...
It is important to share a clear vision of what you
want to the cover to look like. I recommend going through bookstores and
finding the covers that jump out at you. I suggest standing about
20 feet away from a shelf of books and then look at their covers. If they pop
out visually, consider something like them. Then go to Amazon, where most
people will be making the buying-decision for your book, and look at what works for you. And understand why it works for you.
Darkship Thieves and also Orson Scott Card's Ender's Game.
Ender's Game is an interesting book-cover-study. Do a Google image search on the cover. You'll see how cover design has evolved in the last three decades. The cool, angular space ships and funky typefaces of the '80s have been replaced with something that's more personal and more iconic.
You'll want to think a bit about your cover lettering. It should mesh with your story. I picked a Trajan typeface for Finding Time because it was more "timeless" and I used an Algerian typeface for The Aristotelian because it was more "Victorian."
But don't do what I tell you, do what you think works for you.
(You can find the bullet-point outline of How To Publish An Ebook here.)