This article is based on the assumption that you are using a word processing program of some kind in a Windows environment. If you are not using a word processor, the principles will still apply, but they must be implemented manually.
Writing and editing are two totally different tasks. Writing is a creative process, whether the work is fiction or non-fiction. Editing is a critical process. If writers attempt to edit as they write, their creative ability is inhibited. Because each task demands a very specific focus each must be handled separately. Editing should not start until the writing task is completed.
When editing your own work, your eye and mind tend to either fill in, or correct, many errors and, as a result, they are left uncorrected in the manuscript. In order to avoid this, it helps to break any patterns used in creating the original work. If at all possible, the work to be edited should be allowed to "cool off" in a file or desk drawer for a while. The purpose of this is to break the connection between the work and the writers remembrance of the exact words and phrasing used. An additional technique used for breaking this connection is to reformat the work. This can be done by changing the margins, font face and font size, line spacing, etc. This should be an easy task for any word processor.
When saving your work as you edit, the product of each editing session should be saved with a different name. If your original work was called "manuscript.doc," your first save should be called "manuscript1.doc." This means you will always be able to go back and check your original page setup.
If the task of editing is broken down into four (4) steps it becomes less of an onerous task and the result is a much more thorough job.
Run your spell checker without the grammar checker. This seems like the most obvious step however the spell checker can only do part of the job. It will check every word against an internal dictionary and highlight or underline in red, those words that it doesn't find in its dictionary. That means that if you spelled the word "too" and meant to use the world "to" your spell checker will accept either because they are both correct as far as it is concerned.
Spell checkers are normally set to NOT CHECK capitalized words or names, or words with numbers. Ignore these names on your first pass and just correct any misspelled words brought up by the spell checker.
On a second pass with the spell checker, not only verify the spelling of the proper nouns, but also make a note of the correct spelling on a separate piece of paper or in another program. The easiest way to do this is to boot up a text program and multi-task - switching between your manuscript and the text program. This will enable you to quickly verify the spelling of a proper noun throughout your work.
Run the grammar checker. Almost every word processing program has the ability to check grammar and will allow the user to establish both the type of work to be checked along with the specific grammar rules that are to be used during the check. You can set these parameters to fit your need, but remember that your writing style is most important. Don't let the grammar-check program dictate what your style should be. As you go through your manuscript, make those changes, which are obvious problems, such as punctuation, run-on sentences, subject and verb agreement, etc. Don't change your writing style to fit the grammar-checker.
If your manuscript includes dialog, it should be checked for problems with syntax and general usage. The best way to do this is to have someone else read the dialog, out loud, with no voice inflection. Your ear will uncover problems with dialog better than your eye. If you don't have someone else to work with, you will do almost as well by reading the dialog out loud and recording it on some kind of recording device. When you play the dialog back, you will discover problems that your eyes overlooked.
In reviewing writing where there is no dialog, check each paragraph for focus. Is it lean and direct, or are there words that can be removed that will provide a clearer structure? Since this type of problem involves a broader discourse on writing techniques, we can only refer you to the vast number of books on writing that are available for almost every writing project.
Check the overall appearance of your work for uniformity. Have you used the same font face and point size throughout? Is the first line of each paragraph indented the same number of spaces? Is your line spacing consistent? Are your margins consistent? On of the beauties of a good word processor is that once you establish the rules for "page setup" and a "normal" paragraph, and use them throughout your work, you can change the appearance of your entire manuscript by simply changing the settings of either or both rules. This can be extremely helpful if you are submitting the manuscript to several organizations, each of which has different formatting requirements.
If you follow the 4 steps listed above, editing your own writing will be much less difficult and the result will be greatly improved.