and the best, most current advice I can give to any writer seriously considering submitting his-her poetry is to work as an intern or in some slush-reading capacity. It will illuminate your own idiosyncrasies (or what you had assumed were your own special, cute little quirks), and you will grow to despise them.

I'm guilty, more or less, of all of this.
some principles:
1. The two most common types of cover letter are: a) overly minimalist, and b) longer than the submission.
a) address the magazine by name — probably no need to directly address it to a specific editor, but it’s nice to see someone take the time to word-process at least the cover letter. Also, a lack of a cover letter, though not the end of the world, is a minor frustration; see, there’s this thing called priming, and a lack of a cover has roughly the same effect on me as sipping lukewarm coffee while reading it (not good).
b) make sure it is relevant info. I don’t care about your dog. I don’t want you to list every minor publication or accolade you’ve ever received (or worse, almost). Yes, I do read cover letters, but ultimately it is the quality of the work that determines whether or not I pass it on to the editor. In the same vein, do not send what you consider your drafts, second-bests, or good-enoughs my way (this not only makes me question your listing of publications and awards, but inspires very little hope in the whole project itself).
2. On being edgy.
Stop it. Either your thoughts are genuinely interesting and complex, and this is demonstrated by your writing, or they aren’t.
Things that aren’t edgy: bodily fluids/excretions, hating stuff, alternate lifestyles, anything regarding politics, anything regarding religion, anything regarding linguistics/language.
This is not to say there aren’t many fine poems (indeed, some of the better, perhaps the best?) about the above topics — but this impulse seems, perversely, linked to the next point…
3. It’s not the worst subject in the world.
Stop writing about your dog. It’s not that poems about a/your/dogs in general are inherently bad. This more exemplifies the phenomenon of fatigue in a reader. Namely, there are days when it seems that every poem from every contributor is about the same thing. If this happens, then the odds start to stack against your particular poem “about a dog” being the best in the incoming submissions.
I read over a dozen poems today about “what is the soul?” — also, don’t do this. If you write about this, the soul (unless you are Carl Phillips), then stop. Not to say this is not an appropriately “poetic subject”? but that most poems end their conversation at exactly this point. Boringly.
i.e. the poem should not be a meditation on what the soul is (especially if it’s obvious from the poem the writer has some idea), nor should it end with this as a rhetorical device employed to evoke a response from the reader (sympathy in poetry is over-rated), but that it must be genuine (which, is difficult to convey in poetry, and again, ironically, involves craft/crafting).
It is difficult to write about a) the soul, and b) dogs, in a genuine manner.
I really do enjoy the large part of submissions I have had the opportunity to read first. I’m sorry that I can’t offer (or bemoan) some practical and positive advice (it’s always easier to see the negative), but like I said, reading submissions has been illuminating.
In short:
1a. name the publication in your cover letter (and include one)
1b. keep the prior publications/biography relevant (and painlessly brief — also: correctly formatted)
2. reconsider what taking risks means (make sure the risk you are taking is not cliche)
3. give your reader something they haven’t seen before, and aren’t likely to encounter for some time.*
*Really, the only thing to remember is not to submit a fanciful little poem about your pet-peeve, and on the same note: DO NOT submit the poem you just wrote which you consider to be “THE POEM”