1. The first thing your reader sees is your cover letter. Make it work for you. Keep it brief and focused on you as a poet. Don't bother to tell your age (you'd be surprised how many people share this irrelevant information). Also don't list the big name poets you've studied with. Do not be a name dropper!
2. Also do not include in your cover letter any words of praise from other poets or teachers. This will not affect the reader's impression of your work. Definitely do not include blurbs. Why would you already have blurbs, the potential publisher wonders. But feel free to include information about any close acceptances the manuscript has had.
3. If you are asked to provide a description of your manuscript's content in your cover letter, keep that brief and focused. If you find it impossible to describe your manuscript, it's possible that you haven't yet found its center. I see lots of descriptions that list a dozen themes covered in the manuscript: nature, climate change, love, death, religious conversion, pollution, birds, waterways, marriage, children, and so on. Look at that list. Can you find some common themes? Might they suggest a way to tighten up your cover letter—and your manuscript? I also often find that after a list of a number of dark themes, the poet adds a note to the effect that there's also some optimism or that the collection ends with hope. It's not your job to cheer me up. If it's there, fine, but don't force it. I like darkness and so do a lot of other readers.
4. The next thing your reader sees is your title. Don't title your collection with a word no one knows. Why confuse the reader and put a fence around your collection? You can get away with this for an individual poem but not for the collection title.
5. Also regarding titles, there's a trend towards long titles. Go easy here. Some of the ones I've seen just struck me as a kind of strutting, showing off—look at how clever I am! Also very long titles are difficult to format on a cover. This won't get you rejected, but why do it?
6. In your poems, be parsimonious with "how" clauses. I too often see lists of these. This has become an overused strategy. Likewise, avoid overusing "the way" to begin items in a series.
7. Be very sparing with poems about poems. I can take maybe one per manuscript. You won't get rejected if you have more, but if your manuscript is accepted, I will almost certainly ask you to revise some of those poems. I find this kind of poem particularly vexing when the poem is making its way along beautifully on a particular topic and then suddenly starts referring to itself as "this poem." That knocks me right out of the poem. My heart sinks with disappointment.
8. Avoid great blue herons in your poems. I add this here for a light touch, but seriously that bird is so overused in poetry! Surely there are other magnificent birds. And does it have to be a bird?
9. In your Acknowledgments do not include bibliographical information such as page numbers. Just journal titles and poem titles. And be sure to use alphabetical order. Get out a few books by the press you're submitting to and follow the format used for the Acknowledgments in those books. It's pretty standard.
10. Read the Guidelines and follow them. Also read any FAQs that the press provides. Terrapin provides FAQs which should answer most questions submitting poets might have. Yet each submission period brings some chapbook submissions (we don't do chapbooks) and a few New & Selecteds (we also don't do these). Don't waste your time and submission fee by submitting what the press doesn't publish.
11. Terrapin's Guidelines ask that 25%-50% (or more) of the poems in the manuscript have been previously published. Why then submit a manuscript with none of the poems previously published? A few years ago someone who wanted to submit but who hadn't published any of the poems chewed me out about this request. It wasn't his fault, he insisted, that none of his poems had been published; it was the fault of journal editors who wouldn't accept his poems. My argument ended there.
12. Don't wait until the last minute to submit your manuscript. Poets ask if there's any benefit to submitting early or late. Really, no. But lots of poets wait until the last two days of a submission period to submit. Might make the reader cranky. Not me, of course, but maybe some other reader.
13. Get your hands on at least one book by the press you plan to submit to. (If you can't afford to purchase a book or two, at least peruse the Look Inside feature at Amazon for a sample of what the press publishes and how they format a book.) It makes no sense to submit to a press you know nothing about, yet I more than occasionally receive submissions from poets who clearly know nothing about the press.
14. Only submit to a press if you would be happy to be published by that press. If your heart is set on winning a contest, then only submit to contests. A few years ago I accepted a manuscript. The poet stalled her response, then said she'd decided to withdraw as she really wanted to win a contest. She should never have submitted to the press in the first place.
15. Practice Patience and Persistence. Poetry is a slow art. I have a number times received two or even three submissions from the same poet. How is it possible to have that many solid manuscripts in circulation? Consider pulling out the very best poems from the manuscripts and making one new manuscript.