Then, there are those (very, very few) poets who have agents. Someone who does the work for you, who shops your precious book around while you sit back in your recliner and watch reruns of The Office. Which is on all the time now.
Finally, there's the handful of lovely presses which require a query letter sent in lieu of the whole damn book. I have found this system to be the best. Plusses: saving on postage, no contest fee, and being able to tweak the book while it's being considered. And writing the query--a summary of the book, including its theme(s), trajectory, and/or form--is a brilliant way to really get to know your book.
Sure, most of us think we know what the book is about, but only when we sit down and actually try to put it in words do we figure it out. So here's my assignment for you today: write a query for your current project. Try to summarize it in, say, three or four paragraphs...no more than a page. Then re-read your manuscript.
The effect is amazing: out-of-place poems or scenes will stick out like sore thumbs. And you will suddenly know where they are actually supposed to go...or whether (gasp!) they should be cut. What's more, you won't feel bad anymore about cutting them. You will also be able to sense the holes and fill them. Even individual lines or stanzas will show themselves to be in need of revision, all of which will work to make your book more cohesive, more whole.
I don't recommend doing this to a book of poetry or short stories unless you are in the near-final stages of manuscript organization. But those novelists out there might find this useful at any stage of the work.