To stand alone as a sentence, a clause must have a subject and a verb. Comma splicing and other incorrect comma usage. In general, commas separate independent clauses joined by a conjunction. Commas separate items in a series and introductory or parenthetical phrases from the rest of the sentence. Some comma usage is a matter of preference, but even then, one must prefer consistently.
Most students use too many commas.
Incorrect usage of colons and semicolons. A colon is the most abrupt break. Semicolons should be used sparingly to join independent clauses not separated by conjunctions and to replace commas in a series when commas would be confusing. Using apostrophes in plurals and possessives. Know the difference between a plural, a possessive, and a plural possessive.