The English language has complex rules of grammar, usage and syntax. Proper grammar in writing English gives your work an impression of professionalism and therefore lends credibility to your statements. Learning the entirety of English grammar takes years, but observing some simple rules about usage will prevent most common mistakes in writing and improve your style.

Proper Use of Homophones

Common errors in writing revolve around word groups such as "to/two/too," "your/you're" and "affect/effect." These words have drastically different meanings, and using the incorrect word makes a sentence meaningless. "To" is a preposition, "two" is a number and "too" is a conjunction. "Your" is a second-person possessive pronoun, and "you're" is the contraction of "you are." According to Business Writing Tips, "affect" is a verb that means "to change or influence." "Effect" is a noun that means "result or consequence."

Use of Active Voice

Active voice and passive voice refer to sentence structure and how it deals with verbs. Active voice sentences follow the basic subject-verb-object structure, such as "I wrote that book." Passive voice sentences make the object of the verb the subject of the sentence: "The book was written by me." Active voice conveys a more forceful and assertive tone, and makes sentences easier to read. Passive voice, although preferable when referring to an unknown subject, makes sentences wordier. Using "to be" verbs such as "is," "am," "are," "was" and "were" also fall under the use of passive voice. Use them sparingly.

Proper Use of Relative Pronouns

According to English Plus, five relative pronouns connect a subordinate clause to the main part of a sentence: "that," "which," "who," "whose" and "whom." Use "who" as a subject, "whom" as an object and "whose" as the possessive form of "who." The Chicago-Kent College of Law distinguishes "that" as a relative pronoun for restrictive clauses that identify the subject specifically. "Which," however, occurs with nonrestrictive clauses that offer incidental information about the subject without identifying it.

Avoid Misplaced Modifiers

Modifiers--adjectives or adverbs that describe a noun or verb--work best when placed next to the intended subject. Otherwise, the sentence will read awkwardly or illogically. In some cases, misplaced modifiers can alter the meaning of a sentence entirely. The sentence "I only have eyes for you," could have the underlying meaning of "I have eyes for you, but my ears, nose and heart belong to someone else," because the word "only" modifies "eyes." "I have eyes for only you" has "only" modifying "you."