Although there's lots and lots of information on querying, synopses, finding a publisher, etc., there's not a whole lot on what happens after your book is put under contract and before it's published.
I thought this blog entry that is referenced by literary agency Fine Print Literary Management does a good job explaining what's going on (particularly publicity-wise) in the 6 months--1 year before your book hits the shelves: Fine Print blog entry .
These days, the more that the author can do to promote his book, the better. There are plenty of inexpensive means of promotion, like going on a blog tour. There's a wonderful group that discusses promotion and publicity for mystery writers (and other writers) called Murder Must Advertise http://groups.yahoo.com/group/MurderMustAdvertise/ . You have to join the group (it's free) and then you can either view the forums online or you can choose to have them delivered to you by email. They also offer some great tips in their archives on working on publicity before your book is published.