2. The most important key on the keyboard is "delete": Seriously. If your editor tells you to cut--do it. I've worked with academic and creative writers and the best of both know how to "kill their darlings." The best writers know that not every sentence they write is good, and that even if it is the most wonderful sentence ever, it doesn't always belong in a specific book.
3. Grammar is not a feeling: It's not a style or a poetics. It's a system of notation that replicates speech. Periods do certain things. Commas do certain things. And while that magical em-dash can do all sorts of weird things, even it has its limitations. Sure, there's a wee bit of space to break certain rules in fiction, but only certain rules. If your editor tells you something is an error, by all means double-check it. But if it is an error, it needs to go.
4. Editors are on your side: It's true! All those little marks all over your beautiful pages? They're there because we love the work. We want it to be the best it can be. But we're not your mom.
5. Being professional matters: It's unfortunately true. Your query needs to be professional. It needs to look like you know what a query is supposed to be. It should not tell me that you plan to make your book into a movie staring either Angelina Jolie or Penelope Cruz. It should not tell me that this is your very first special and shiny try at writing or that you writing whenever you get time. It is the equivalent of a job interview.