Whether you're writing an essay, a book, a marketing brochure or website content, the most important step of the writing process is not in the planning of what you're going to write, and it's not in the choice of tone, style or language; the most important step is in fact the editing. As a writer therefore it's important to appreciate the significance of the editing process and to some extent be able to edit your own work.
The editing process is a systematic way to get the best out of your writing; it involves recognising weaknesses in your use of language, plot, characterisation, dialogue etcetera, as well as identifying the strong areas and realising themes that can be expanded. The editing process should also include the basic proofreading elements of checking for spelling mistakes and grammar errors.
It is often difficult for a writer to edit their own work well as the more time they spend on their writing the closer they become to it. An editor requires a certain amount of distance from the work they are editing to ensure they can get the best from the text they are working on. It is often the case that a fresh pair of eyes will quickly pick up inconsistencies or errors that the writer has missed, because the writer knows what they are expecting to read and their mind generally fills in the blanks or skims over the mistakes. This is why using a professional copy editor is often preferable to trying to edit yourself. This does not however mean that a writer can not be involved in the editing process; in fact it is often better if the process is a joint effort between writer and editor, allowing for the editor to make suggestions or prompt the writer to think of alternative ways to convey their message. The writer can subsequently develop their own work, in their own style as a result of the editor's comments.
Many writers find that although their first draft of a manuscript, poem or essay, holds all of the basic elements that they which to express in their work, it may be many edits down the line before they are finally happy with the finished result. This is not a reflection of the writer's natural ability or technical skill, indeed a good writer is one who is willing to edit, edit and edit again; this commitment to a project will pay dividends in the end, causing a writer to produce work that far surpasses the efforts of a first draft.