I am a professional marketer and here are a few suggestions:
1. Understand who your target audience is - your "perfect" customers
2. Find out where they gather online - forums, blogs they read, web sites they hang out on
3. Get conversion tracking in place so you know where each sale comes from (Do NOT skip this step)
4. Buy advertising on these sites or ask the blog owner if they would review your ebook
5. Build a list of your readers on your own web site so that you can tell them when you have new releases. Let them subscribe via email, Facebook, Twitter, etc.