Even the greenest of graduate students have heard "publish or perish," but rarely are they instructed on exactly how to accomplish that or even where to start. The world of publishing can feel intimidating to those who've already pumped out a few books, let alone the uninitiated.
To find your way into this world, you must gain access to the gatekeepers - that is, get your idea in front of book editors. How you do that depends on whether you are approaching an academic press or a commercial "trade" publisher. I'll focus here on university and other scholarly presses because that is the most common path to publication for Ph.D.s.