The document discusses common sentence errors such as fragments, run-on sentences, and comma splices. Sentence fragments are missing either a subject or a verb. Run-on sentences incorrectly connect two independent clauses with no punctuation. Comma splices incorrectly use commas instead of conjunctions like "and", "but", or "however" to connect two independent clauses. The best way to avoid these errors is to ensure each idea is expressed in a complete sentence with both a subject and a verb.