What is your best advice?
I advertise on FaceBook by mentioning my books in my page when they are released or revised. The link sends potential readers to the book's page in my Lulu author's profile, where they can read a sample. Costs me nothing. Google Books also advertises them freely and offers a sample so that potential readers can have an idea of what's inside. Babelio and other readers' sites advertise some of my books: I have no idea as to whom I owe this service. All distributors like Amazon, Barnes and Nobles, sort of advertise them through Google. Finally, if I enter Ingram and ask for a title of mine, I can see the list of on-line stores selling brand new copies and second-hand copies with their prices. Curiously enough, some obsolete editions are offered at a higher price than the new revised ones.
I have tried video, reviews, blogging, social media, promoting here, interviews, and so on.
And I found the only thing that works is a great title, a great cleanly formatted interior, a unique idea, well written, error free, fantastic description, and a superb cover.
The marketing then pretty much does itself. I have sold more books by having a great product than any other gimmick.