Before you can sell any book in the Internet, you must understand at once that to sell books, and so that you can download for free. For the sale of such books must, at least, place them on a mass resource, dedicated to such topics (for example, http://www.ozon.ru). Moreover, books are probably available on such resources are already posted. But even if you're lucky, and the book will be posted, still not the fact that somebody will buy it.
More chances to sell the book online promises its originality, inaccessibility. Also in this respect adds to the chances that personal. But if the book is not yours, and could theoretically be placed on the Internet, you need to ensure immediately that it is not available for free. Check this preferably with the help of any search engine.
Before you sell not yet available in the electronic version of the book, you need to do the promotion. Every book has its own theme, so the announcement that the electronic version is desirable to publish in thematic communities, forums, groups, portals, etc. And still need to write the announcement, and even better a few pages for review. In case of interest you can either continue PR (create a page on the Internet, a group in the social network), or to start selling.
Sometimes books pay and download directly from sites immediately, not wanting to waste time searching for the free version, so it is best to sell both on public resources (for example, http://www.litres.ru), and thematic. Also the book can be translated to other formats (e.g. for mobile phone, PDA, etc.). and to sell on the wap sites.