Some ways to correct one's grammar are understanding advanced grammar rules and improving word usage. Some examples of advanced grammar rules are the subjunctive mood and parallel structure. A common word choice error is confusing "which" and "that."
Some other advanced grammar rules involve the possessive case with gerunds, splitting infinitives, reflexive pronouns, placement of the word "only" and ending sentences with prepositions.
A few common word choice errors include confusing "who" and "whom," "sit" and "set," "lay" and "lie," "effect" and "affect" and "less" and "fewer."
Other ways to improve grammar are proper usage of capitalization, hyphenation, apostrophes, quotation marks and punctuation marks such as the comma, semicolon, colon and period.