Once your ebook is finished, or even while you are still writing and editing, begin to visit groups and forums that are related to your niche in some way. These sites are great for connecting with people who will be interested in your topic and may want to purchase your ebook and other services. You can find these forums and groups by searching for your niche plus the word group or forum in the search engines.
It is best to register as a member and then spend some time just reading what people are talking about before you make any posts. Do this for at least a week. See what their struggles and complaints are and then you will be able to make comments to solve their problems. Your signature line is key here – you can’t blatantly promote what you do, but a well written signature line will say it all.