I have been using the following strategies successfully:
1. Advertising in weekly magazines that relate to a city eg, Melbourne, Australia. (People pick this up free and read it on the way to work)
2. Pay per click advertising with Google Adwords (targeted keywords)
3. Targeting online retailers with complementary products/services and arranging links from their sites to mine, usually with an affiliate payment for referred purchases
Depending on how much money you want to spend and the title of the book, there are other ways to do it, but the above bring me in a regular flow weekly.