If you write long enough and produce enough work, you'll eventually have books in your back catalog that just aren't selling any more. One or two people may discover them in a month, but they're mostly gathering virtual dust on your virtual shelves. It's not that they're bad books, it's just that readers are constantly looking for newer and shinier things. Instead of wasting all the effort it took to write these older books, why not relaunch them to find a brand new set of fans? Rebranding your work can turn obscure titles on your list into exciting new moneymakers with relatively little effort. 
First Things First
Look through your back catalog and find a coherent group of books that belong together. It's best if they're in a series, but it will work if they're just in the same genre. The idea is to release them as a concise set, all tied together to entice readers to buy one after another. Once you have the books picked out, unpublish all of them on every venue. You're going to be starting all over, and it won't work if the older version of the books is still for sale on even the smallest venue.
Do Your Research
The bestselling books today are genre books: romance, science fiction, western and the like. What niche does your group of books fit in? Look through the ebook listings on Amazon to get a better idea of how these genres break down. Once you figure out exactly where your books fit, study the top 100 books in that niche. Look at what the covers look like, check for keywords, read the blurbs and even look for the authors' names. You'll begin to see patterns at every step. Take ideas from these bestsellers and apply them to your books.
Build Your Brand
Redo your book collection as a group, and aim each part of the renewal toward the top 100 books in your genre. Hire a book cover designer to create a series of covers that go together as a group. Make a list of keywords that match up with the best selling books in your niche. Write new book blurbs that match today's best books in style and content. When it's done, you'll have an entirely new book collection aimed toward today's eager reader.
Launch Your Books
Publish the first book in your series, then wait 3-6 weeks before publishing the next. This allows each current book to shine, then a new book to take over when the older one begins to fade in popularity. Continue with this pattern until you've published the entire series.
Keep the Faith and May the Force be with You!
