The best part of decorating with books is that it can be so easy and with really great results.
One option (that I have tried myself) is arranging books according to the cover colour. This is really fun actually - it means collecting all your books (and maybe some other details like vases, boxes, etc.) and putting them in same colour group. The visual impact is lovely and immediately your bookcase becomes a centerpiece of the room!
image sources 1,2,3,4,5,6,7,8,9
The possibilities of playing with colours (and objects) are many. If you have lots of books though, I suggest remembering which colour the cover was in case you need it later ;))
For the braver ones, there is another lovely solution. Paint (or use wallpaper) on the wall/board behind. This is quite easy to do as the surface is probably not big, so even the wallpaper wouldn't be an expensive option. I guess that in some cases you could use a beautiful decorative paper instead.
The colour is usually either a few shades darker than the rest of the walls (decorators' trick) or a contrasty one.
image sources: 1,2,3,4,5,6,7,8,9
If you want the opposite - to make your bookcase neutral and neat, and despair because of the book covers colours - here's the solution: Turn your books around!
I know most of us wouldn't do this, but you have to admit - it looks great!
And me, oh I am dreaming about a simple reading nook with a lovely view. Something perfect like this (and a cup of coffee around). I would replace the box though ;)