How important is marketing?

I've read that writing a book is 10% of the effort and that marketing, the other 90%, is the key to an authors success. What are your thoughts on how to market a book?

I'm regularly on the lookout for positive suggestions on how to market my books and grow an audience of happy readers.

I've recently started utilizing video trailers for my books and I'm looking forward to sharing the results of that marketing approach as data becomes available.

Please leave any ideas that you may have here.

Well, the book trailer was a seemingly Great idea but you have to figure out how to get people to see it. Easier said than done.

Moving on to the next idea