This article is largely for self-publishers. If you are having a hard time making your book look more appealing, then it may be time to start on the side of thievery.
People come up with good ideas all the time for books and graphics and art. If you think your book looks bland, then chances are it does.
ENGAGING, NOT BUSY
I told a friend one time to go through the bookstore to see what other authors had on their covers. What type of graphics were displayed and what kind of font used. The front cover should be engaging, not busy. Busy isn't horrible for book covers; but think of magazine covers. Busy isn't great for those, so try to institute that mentality for your book cover. A simple photo in black and white. A solo object that symbolizes the story. Black background with the title in gray letters. Or red letters. Or blue, white, yellow—any color.
FIND A GRAPHIC ARTIST
And if you can't think of a way or find an example of how to make the front, back and side of your book look appealing, then find yourself a good graphic artist and hand that project off to them. Can't afford a graphic artist? Of course you can. Find one in college. Those students are always looking for ways to add to their portfolio. Don't know any college students? Then that's normal. Go to the local college and find one. Don't want to search for one? Then get a blank piece of paper and a pencil, draw your own graphic, and call yourself innovative. Or you could get off your lazy butt and find an artist. Or stop being cheap and pay one.