What an editor needs from a writer

 As an undergraduate I aimed to become a writer of fiction. Experience proved that I lack imagination. But for nonfiction prose--articles, letters, memos--I can tell you things you need to know. 

Don't be afraid of revising. You may need time to puzzle out what you mean to say, and then how to say it effectively. You may need to take an entirely different approach than your first one. You may decide that material you included is not helpful and needs to be cut. You may need to suss out additional material. Keep at it. 

Decide what you mean to say. You should identify the One Main Thing in your article/letter/memo. It needs to have a single principal idea or element, through there may be any number of subsidiary ideas or elements. 

Say that One Main Thing in a single sentence. When you can do that, you know what your focus is. Use that sentence.

Say it up front. You may want some introductory sentences, but in the name of God keep them short. Your reader wants to know very early on what this is all about--and deserves to know that. Treat your text as if it were classical epic beginning in medias res, right where things are important now. 

Keep the background where it belongs. As a teenager working for my local paper in Kentucky I once attended a county government meeting. As the members of the fiscal court listened, the county judge spat tobacco juice into a coffee can, and I took notes, an elderly Baptist divine launched an extended narrative that involved multiple people over a considerable span of time. Some minutes into it, I gathered that he was appearing to request a fresh load of gravel on a stretch of road. 

Bring the background up after your main idea is well established, and only then if it is really germane. 

Don't screw up the chronology. Your reader needs to be oriented in place and time at every point in your text, particularly if you get fancy with the narrative and switch from the present to the past and back. 

Organize your subtopics. Each of those subsidiary ideas or elements should be addressed in a paragraph or set of paragraphs, in what appears to the reader to be a logical order, with transitions from one to the next. This is also part of the reader's orientation. 

Choose the diction that is appropriate to your subject and your reader(s). There's a lot of room in English, from the most formal to the most colloquial, and you can plot where on that broad continuum you can most effectively say what you want the reader to understand. (Read it out loud to yourself; that should help you identify language that doesn't work.)

Give it a final read for the little stuff. You know, the spelling (particularly of names), the punctuation, the grammar, the usage. That stuff. 

The consequence: Neglect any of these things, and it will fall to me to fix them, and I'm good at what I do. I charge for it. But you would probably prefer to say what you mean yourself, clearly and effectively, rather than have me attempt to guess what you mean.