Check out this blog, about the best and worst advice a writer, Michelle Gagnon, received. It provides a down-to-earth take on so many lunatic ideas about promotion, and also offers advice on what does work to sell books.
What I loved best was the second comment below the post: "The only thing you have control over is your writing."
In other words write your best. That is in your hands. Don’t waste excessive energy trying to promote to the point of insanity/vanity – that’s what self-published writers do because they prefer to put their energies into promotion than towards perfecting their craft. Maybe because they’re better at it? So don’t squander valuable thinking space and time with activities peripheral to what does matter – the writing.
For what it’s worth, here is what Michelle Gagnon cites from a report as being the most significant factors in book purchase:
-Recommendation from someone I know
-Saw on a bestseller list
-Reviews you've read in blogs/online forums
-Reviews you read in magazines/newspapers
-Prominent display in bookstore
Most of those are out of your control. What you can control is writing your darndest.