You will sell more eBooks when you tell people how to solve the problems they have that are related to your niche. People will do more to alleviate their pain than they will to gain pleasure. The whole idea of being able to download an eBook from the internet at any hour of the day is based on the premise that people want answers to their problems immediately.
For example, if your niche is parenting infants and toddlers, you may be writing an eBook about how to have a happy and well-adjusted child. Parents will be interested in that type of information, but imagine their little one has an earache. Can you see how much more motivated they would be to purchase information on how to solve that problem when their baby is crying from the pain?
Think about the people in your target audience. What keeps them awake at night? What problems are they facing that you could help them with? Answer those questions and include them in an eBook.