I've found that Pinterest is a great way to distract myself from writing, but if you can manage to stay a little more professional than me it's also a great marketing tool. Pinterest and self-publishing were made for each other, in fact. It's a little site that became huge, and it's driven by ordinary people who are simply sharing what they like. If that doesn't have indie written all over it...what does?
Get on Board(s)
I belong to several boards about books and reading, and I created my own boards to show off book covers, book blogs I like, books I've reviewed and books I love. There are a ton of book-oriented boards you can get into on Pinterest, but you can also take it one step further...and I think you should.
Pinterest is great for sharing book covers, but please don't stop there. If you really want to promote your book, use the site to start building that world online. I've seen authors who create Pinterest boards for character weddings, for character closets (pictures of clothing and accessories and shoes), maybe even for the character itself (foods, hobbies, interests that represent that character). You can even build boards to represent the specific setting where your book takes place.
That's the great thing about Pinterest -- you can pin just about any photo, any time. Show me the car your character drives. Show me a girl or boy who looks like them. I want to see the house they live in, the hairstyles they use. Do they have a tattoo? A pet? A unique talent? Pin it to your book board! Take your readers deeper into your world, and take your promotions further.