- Titles: If your piece is talking about people a lot, make a point to check that all their titles are consistent. For example, Robert Drumgool, Ph.D., and Dr. Robert Drumgool are both right, but you should strive to only use one form. Another example is the Ms. versus Miss title; Ms. implies a desire to not be classified based on marital status and Miss implies never having been married.
- Capitalization: Check for consistency with capitalizing names of organizations, departments, ideas, theories, etc. This is particularly crucial if what is being capitalized is not commonly capitalized but you have a specific reason for wanting it to be so. For example, if your piece is about Rogers University and you decide to capitalize University whenever it refers to Rogers University, you might not notice if one instance goes uncapitalized, since that word is usually not.
- British/American Spelling: As the Oxford Dictionary shows, there are several instances where British and American spelling is different. Make sure that you are using one or the other and check for its consistency. The issue I come across the most with this is the omitting of the second l in some American English words (traveled versus travelled), since American English does double other consonants when changing tenses (omitted, for example).
- Alternate Spellings: A great example of this is advisor/adviser or grey/gray; this is not an example of a British/American divide, but rather two acceptable versions of the same word. Since we are familiar with both spellings, it can be easy to interchange them on accident; but when you're editing your document, check to make sure that your use of one or the other is consistent.
- Numerals/Numbers: All manuals of style have rules about when to use numerals and when to spell out numbers. If you're following a manual, refresh yourself on the rules and stick to them. If you're not following a manual, choose a rule (spell out under ten, spell out one- or two-word numbers, etc.) and stick with it.
The key for all this is ensuring credibility; readers are more willing to trust writers who provide them consistency (after all, isn't stability one of those basic human needs?). Pay attention to the details. They matter. :)