You begin, frankly, by being part of a poetic community. There thousands of books of poetry published every year in the U.S.--and that's
trade publishers, never mind self- and vanity publishing (and there are some good self-published collections out there). Most of those authors make good-faith attempts to move copies of their books. One is asked to "like" books one has never read on Facebook; as a magazine associate editor, I am frequently queried about reviewing books by authors we've never published--and we can generally fit in four books per issue. I am, on the editorial and buying side of things, more likely to buy a book if I know the author's work already, whether due to a personal acquaintance (and I buy a fair number of books at readings), or through reading, usually in publications I rate to one degree or another--PMing me every draft of every poem you write without checking if it's okay is a good way to get your drafts deleted without my opening them. Or in some cases, I read articles or reviews that sound interesting, or I'm intrigued by the "buzz" around a book. Deciding to go ahead and commission, edit, and print a review is similar.
"Getting involved" can happen in many ways. Take, for example, this place. Getting a rep as a good reader and writer will move books online as well--but one has to put in the legwork. Similarly with live readings, it helps to regularly attend the things if one wants to ask for features. More generally, though, this is my experience (the math's a bit off toward the end, but the principle applies):
http://www.cprw.com/the-lighter-side...ur-poetry-book