A good knowledge of the English language includes the understanding nouns, verbs and various types of verbs, adverbs, adjectives, contractions, pronouns, prepositions, possessive pronouns, synonyms, antonyms, predicates, sentence structures (including simple, compound, complex and compound-complex).  In addition, you should have a good grasp on knowing punctuation marks such as the period, question mark, exclamation point, colons, semicolons, commas, quotation marks and more, as well as their correct usage and their placements in writing.