First I would like to go on record as saying, it is a good idea to have your book cover professionally designed. After all, we as self-published Indie Writers/Authors are directly competing with multi-million dollar publishing agencies with years of experience in selling books. Our book covers need to look at least as good as theirs. At least, that's what I'm told.
Ok, I admit it. I have never had my covers professionally designed. I have always created them myself with an easy-to-learn, inexpensive desktop publishing program.
I use PrintShop, but I'm sure any of the brand name desktop publisher would do. The trick is to find just the right photo or combination of photos for your book.
As I said in other places in this website, as an Indie Author, I carry a camera with me everywhere I go and I snap LOTS of pictures. You never know when you will snap a picture that will work as a beautiful cover for your book. Invest in a camera that makes nice pictures rather than relying on your cell phone, as you will need a good, high-quality file if it is to look professional on a book cover.
You also have the option of going to a stock photo site and purchasing a nice picture for around $3 bucks. This is an excellent option if you have no plans for printing your book on demand. However, if you are going to sell multiple copies of that photo on your printed book covers, you will be required to purchase the bigger license for that photo and it will cost you quite a bit more.
Sometimes you might even be lucky enough to find a royalty-free picture online. Paintings by long-gone artists sometimes look great on the cover of a historical romance book.
Once you have decided on your cover-design picture, import it into your desktop publishing program. Check the self-publishing sites where you plan to publish your book to see what their requirements are as far as dimensions for your cover art and crop your picture accordingly. (Don't forget to leave sufficient space along the edges for "bleed.") Then add your title and play with fonts until until it looks just right. Don't forget to place your author name on the cover, as well.
Save the whole thing as a pdf and use this when you're uploading to the self-publishing sites. Using their software, you should be able to match the back of the book and side of the book to the cover you have created, then add your description.
On a side note... many of the self-publishing companies have pre-made book covers for your use. If you use these, however, it is a good idea to customize them. You don't want your book to look just like someone else's, do you? Plus, you will have to design a different book cover for every site on which you publish your book. That sometimes makes it confusing for customers who are looking for your book.
As I said before, it is BEST to have your cover professionally designed, but if you have a vision of your own, or if you're like me and just plain can't afford it, your best option is to learn desktop publishing.
Designing a Book Cover