Before submitting or distributing your essay, research report, email, or any other document, besides performing the usual spell checking and proofreading, you should make certain that your writing is consistent in terms of spellings, usages, and formatting. This is important for two reasons: it helps to guarantee the clarity of your message and it lends an appearance of professionalism to your document.
If, for example, you refer to “theatres” in one part of your paper, you should not use “theaters” in another section. Neither should you vary from “U.S.A.” to “USA” or from “Prof.” to “Professor.” This also applies to names. For example, be careful to spell “Thompson” the same way throughout your paper, and not as “Thomson” and “Tompson.”
You should also make sure you are consistent in reference to your use of numerals and letters in lists. If you use a numbered or lettered list in one section of your paper, maintain that usage later on. You must also be consistent in reference to your use of capital and lower case letters in titles and lists and headings. For example, you may decide to use all capitals in headings and titles, except for articles and prepositions (assuming this is in accordance with the formatting style you are using), as in the following: Some of the Causes of the Civil War. Therefore, similar subsequent headings should be written according to that style. And so, the following would be incorrect: Early battles during the first months of the war.
Consistency applies to spacing and paragraphing too. You should use the same number of spaces between sentences. The common practice is to insert one space between sentences, but two is also acceptable. Of course, if you use block formatting (where all lines of text end at the right margin), then the spaces between sentences (and between words) will vary.
In addition, you should make sure that all of your paragraphs begin in the same formatting manner: that is indented or left justified, and not a mixture of both styles.
Consistency applies to citations and references lists. Do not vary between MLA, APA, Chicago, and other formatting styles. Choose one, and use only that one.
In short, to ensure that your written work represents your best efforts, you must maintain consistency at all times.