Summarize this article in one sentence.
People always like to get something free. You can offer some related item or incentive to increase the odds that people will purchase the eBook.  This is a particularly good strategy if you have other eBooks that you've written. You can offer access to one of these books for free with the purchase of your new book. Keep in mind that you should never offer something for free that will cost you a lot of money. If the cost of the free gift is more than the profit you'll make on the eBook, you will put yourself in the hole financially! An affiliate program is a system to gain referrals in exchange for a commission. Members of your affiliate program will receive a small incentive to promote your book for you.. For instance, a popular lifestyle blogger might recommend your eBook and provide a referral link to her readers, and she will earn a 10% commission on sales that result from site traffic and purchases using that referral link.  You need to ensure that the price of your eBook can justify paying commissions. A book that sells for $0.99, for example, can only afford a few penny's worth of commission for referrals. You can ask friends, family, or members of your writing club to serve as affiliates, but the most affective online affiliates are those with a substantial blog or social media presence. Search engine optimization (SEO) is a way to ensure that when people search the internet using popular search engines, your eBook will show up in the suggested results. For instance, if you've written an eBook about changing tires, your eBook website would show up in the first page of search results when a person typed in the search query "how to change a tire."  To take advantage of search engine optimization, you need to make sure your eBook or author website uses the right terms and phrases, known as keywords, to drive traffic to your site.  Start by creating a very extensive list of all the possible search engine queries a person may use who would benefit from your eBook. In the example of an eBook on changing tires, you might include makes and models of cars included in your guide; popular brands of tires; words like tire, car, maintenance, mechanic, service; and others. Next, update your website using these words as much as possible, in the actual text visible to readers (the "front page") and the indexing system you use on the "back page" as you write the website. You still want your website to be helpful, reader-friendly, and attractive, so be careful to keep it sounding natural. If you are uncomfortable with website design, you can hire a consultant to build your site and ensure that SEO drives traffic to your site..

Summary:
Offer a bonus item or another incentive to purchase now. Create an affiliate program so that others will promote your eBook. Use  search engine optimization to drive traffic to your website.