The final thing that I think is so important to be in the know about is the publisher you're targeting. Even knowing what the editor likes is important. Pen Pen mentioned reading books and discovering the author's agent through that; the same thing can be done for editors.
When reading a book similar in style to yours, check out if there's an editor acknowledgement. Go online and read editor interviews. Most of the time we only have one chance to submit to an editor so it's important that we pick the one most likely to connect with our writing.
You all know I just got a rejection back on The Bad Boy's Redemption. I learned a very valuable lesson with that story.
Basically, Love Inspired publishes books with plots revolving around small town and family. I've read tons of LI books and I studied the pacing, the length, the setup, but never the plotlines.
My mistake. The editor who rejected me was kind enough to mention stuff I should've already known, if I would've studied the publisher better.
You may have an awesome story, with spine-tingling writing, but if the publisher you submit to doesn't publish that kind of book, then it's a useless submission. The writing and the story won't matter.
Have you ever subbed to the wrong place? Or realized that no publisher is printing the kind of story you write? What's your favorite way to research editors? Or do you leave that up to your agent?