As the managing editor of a historical fiction imprint, lately I've been seeing it all when it comes to manuscript submissions. Editors are busy people — especially ones like me who are trying to juggle editing with another full-time job like writing — so it's in the author's interest to make their job as easy as possible. Why, you ask?
Because if you make it hard for them, they're going to be less inclined to accept your manuscript. Trust me.
The most important part of this process is to FOLLOW THE SUBMISSION GUIDELINES. I can't stress this enough. Don't get creative; don't think those guidelines apply to everyone BUT you. They don't. If the guidelines ask for a query letter and the first chapter embedded in the email, don't send a blank email with no letter and the whole manuscript as an attachment. Those submissions hit the auto-reject pile as fast as I open the email.
Don't send a first draft. Ever. Seriously. All you'll do is burn the opportunity for publication with that editor forever. If I open a manuscript that's riddled with grammatical and spelling errors, where pet constructions are used to death and the story begins with a BIG infodump, flashback, or dream sequence, I know it's not been properly edited or proofed. That manuscript also hits the auto-reject pile pretty darn fast.
Edit and proof your manuscript by hand, going line by line with a good style book like the Chicago Manual of Style. Spell check is not a substitute for proofing your work yourself. Most people don't realize that spell check can't catch common mistakes — like homonym errors. Your/you're errors or to/two/too errors turn this editor off quickly. Here again, I know the manuscript hasn't been properly edited or proofed. And every such error means more work and time on the part of my staff, sometimes to the point where it's insurmountable. Proofing is part of a writer's job, a part that's all too often ignored. Why take a chance?