March 16 - Start marketing early. Don't wait until you have books in your hands to start building a following for your book. Keeping your book a secret is not going to protect you -- in fact it is the most dangerous thing you can do. There is little risk to most authors of someone stealing your idea - everyone wants to write their own book with their own idea.
People aren't going to just line up when your book comes off the press -- you have to get their attention and their buy in. Make it a book they anticipate and look forward to.
If you are doing non-fiction or children's books, it's not too early to start chatting up your upcoming book 12 to 18 months prior to your book coming out.
If you are self publishing fiction, start building social media and other vehicles 8 months to 2 years ahead ahead of it's publication.
Actively market during this time. You can't get the time before your publication date back. Once the book is out, it's out!