If you're self-published, one of the things you need to think about is what you want for your cover.
Obviously, if money is an issue, your options are severely limited to what images you can find on free sites like Wikimedia Commons and Morguefile.com and what you can do with your own skill level in photoshop.
Some people cheat and try to rip ready made artwork off of Google, but seriously, don't do that. You're opening yourself up to a whole world of litigation.
It can be difficult for writers to come up with ideas that illustrate enough of the story to entice people, without giving away major plot points. Art can be abstract, or practical, depending on the preferences of the artist and the one commissioning the work.
Now, I've been a fan of the card game Magic: The Gathering for years. There are easily 30,000 different cards, each with different art. Art that I've seen self-published authors take and try to pass off for their covers, and I have no problem admitting that I've reported them when I've spotted them.
The most recent set of cards is about a city that emulates ancient Egypt, and it has some incredible art. But the art itself isn't why I'm bringing this up. See, the company that makes the card game, posts articles on their website every day, a lot of which are behind the scenes, and one of the articles that have always intrigued me is the concept of the art.
These articles give us a view from the inside, where they commission the art for their cards with sometimes specific, sometimes vague descriptions, and let the artists take it from there.
Check them out here, and here.
If you check out the links, I think you'll see what I'm getting at. If you hire someone to do art for your cover, it pays to have an idea, but the more information you can give them, things like setting, mood, focus, the better your art will give you what you're looking for even if you give the artist some leeway.
If you're having trouble coming up with an idea for a cover, it's also a good way to get some things going. Start with the mood of the cover, or the genre, and then move on to the setting, then the focus, etc. etc. This also lets you envision the cover in the way that we authors see best, with words.
Just remember, when you hire an artist, you want your money's worth, and the easiest way to lose out is to not have an idea or direction for them to work from. Hired artists aren't going to look at your book and come up with a great cover for you on their own.