1. Anticipate objections your visitors might have about your free ebook offer. You should research your target audience's needs and wants.
2. Allow your visitors to feel good about themselves by giving them compliments. If they feel good, they will also feel good about downloading your ebook.
3. Tell your visitors emotional and logical reasons why they should download your free ebook. It can be goals they'll acomplish, positive feelings, etc.
4. Publish a list of respected or famous people that have downloaded your free ebook. Just remember to get their legal permission first.
5. Tell people what they're thinking and feeling as they read your ebook ad. Most people will start to actually do it, statements should back up ebook.
6. Make your free ebook offer very rare. People perceive things that are rare as being more valuable. You could use a limited time offer or free bonuses.