You can spend $97 for a marketing book you find listed first when you Google the terms "How to Market Your E-book" or you can peruse these tips for free: I'm going to assume here that you wrote a good ebook, made sure it was edited for content and grammar and have uploaded it to several retail sites (e.g., Amazon, iBookstore, Barnes & Noble). Assuming that starting point, try the following.
1. Pay to have someone create a cover for your ebook that is graphic and eye-catching.
2. Write a succinct book AND author description for your e-book that includes keywords related to the subject of your ebook.
3. Upload a sample of your book to Wattpad, Scribd and other community reading sites to generate initial impressions and buzz.
4. Send free versions of your ebook to friends and ask them to write reviews for you on the retailer sites where you sell your ebook. (Note: Amazon is clamping down on this, but reviews still matter.)
5. Use Twitter, Facebook and LinkedIn to announce your ebook for sale often. But remember to post interesting items not related to your book in-between your announcements.
6. Write a blog post about your ebook.
7. Submit your ebook to be reviewed on subject related websites and blogs.
8. Email your network of friends, relatives and colleagues to announce the book is on sale.
9. Include links to your ebooks on sale in your email signature block.
10. Mention your ebook on forums or community boards related to the subject of your book.
11. Set a competitive price for your ebook and then experiment with changing the price.
12. Create a video for your ebook. You can do a trailer or an author interview or even a making of the ebook video.
13. Timing. Release your ebook and grow its sales just before consumers traditionally expect it. For example, weight loss books are usually sold in January so if you were selling a weight loss book you'd want to get it out into the market a few weeks before New Year's Eve.
14. Offer incentives or give-aways to ebook purchasers.
15. Do a give-away on Goodreads (you just need an author account).
What am I missing? What have you done that's been effective?