In most writing, common mistakes include:

• incorrect use of punctuation, including commas, semicolons, colons, and dashes, etc.
• misusing articles and prepositions
• creating hazy antecedents ("Running across the street, a snowball hit him on the head."  Who or what was running?)
• mistaking one word for another (envelope and envelop, stationary and stationery, affect and effect, complement and compliment). The spell-checker won't detect these errors.
• confusing "then" and "than," "its" and "it's," "affect" and "effect," and "lay" and "lie"
• creating sentences that run on and on and on and don't stop even when they should but instead they keep going, getting every possible ramification in and each and every circumstance that may be part of the original idea which by now we have forgotten anyway, but it's all part of the same idea still, isn't it?

• light formatting
• correcting spelling, grammar, and punctuation
• correcting usage errors, subject/verb agreement, misused prepositions, dangling participles, misplaced modifiers, confusion in tense, faulty parallelism, etc.
• correcting redundancy
• correcting inconsistencies in headings, tables, figures, and lists
• substituting words that more accurately convey the author's intent, but without making changes that are unnecessary
• avoiding sexism, racism, or other pejorative language
• maintaining consistent patterns for abbreviations, etc.

• correcting errors in spelling, usage, grammar, punctuation, and style.
• correcting fluctuations in tense, faulty parallelism, misused pronouns, etc.
• clarifying ambiguous vocabulary
• eliminating redundancies
• replacing jargon and cliches
• noting inconsistencies in the writing voice or point of view
• identifying inconsistencies in logic, facts, and details
• revising or cutting to meet length requirements

• reviewing the flow and organization of text
• recognizing structure appropriate for the intended audience. Suggesting deletions, additions, or rearrangements (e.g., gaps in content, missing steps in the argument, unclear transitions).
• creating an outline to reveal structure
• reorganizing material into an appropriate structure and sequence
• recognizing when material would be better presented in another form (e.g., number-laden text as a table or chart, descriptive material as a diagram or illustration, a long series of points as a list)

• ensuring that sources are acknowledged in a form appropriate to the publication
• noting the essential information that must appear in a periodical (date of issue, volume and number, publisher's name and address)

• adjusting variations within row and columnheads and the presentation of data
• ensuring that non-text items (e.g., tables, figures, photos) appear in the correct position and fit the given space

• correcting inconsistencies or errors in spelling, grammar, punctuation, or fact
• checking or constructing a Table of Contents
• correcting errors that result from the use of spell-checkers, (e.g., substitution of 'too' for 'to' or 'film' for 'file')
• using fonts, font sizes, and typefaces consistently
• setting margins as justified or ragged