Getting the word out about your upcoming book becomes an important aspect of sales. Your ability to do this is important when you offer a book to a publisher or promote your own self-published one. In fact, most publishers these days look for your information about your ability to promote when you send them a proposal.
Starting a blog about your book has become very popular. The time to start it is long before the book is published. In fact, many authors use a blog to talk about their book before it's submitted to a publisher or they have it in print or e-book form.
However, when doing this, make sure it's a book whose idea can't be stolen. Give out hints, but not the unique aspects. Develop curiosity and interest, but retain the details.
I'm developing a blog, Plymouth, NH...250th Anniversary, for my upcoming book, Plymouth of Yesteryear, a compilation of my previously published columns and articles (of which I've retained the rights) for newspapers and magazines about the history of the Plymouth, NH area. I've pondered on this idea for quite some time but never got the wheels in motion. Yes, I did approach a regional publisher, only to have him tell me he didn't think there was wide enough readership for it to be worthwhile for him.
In 2012, Plymouth, the town where I live, will be celebrating it's 250th anniversary. This seems to be the appropriate time for publication. Also, I've decided upon self-publication. (I've done this before with a children's anthology of my previously published stories.) It seems practical since a local printer, who helped me with the other book, has print on demand capabilities. Thus, I don't have to contract for multiple copies and put out extensive funds.
I can promote the book along with activities and events sponsored by the local historical society. I can give talks to local groups. I can hold book signings at local bookstores and other places of business. I can provide workshops on history and writing.
I'm starting with my blog to begin promotion and for referring interested parties. They can watch the progress of my book. Also, I can begin to take pre-orders.
So...think about using your blog or setting up one to begin promotion of your book, too. Many well-known authors have used this technique.