The document discusses three types of mixed constructions: dependent clauses, prepositional phrases, and independent clauses. It provides an example of each used incorrectly, followed by a revised correct version. Specifically, it addresses how dependent clauses, prepositional phrases, and independent clauses should not be used to start a sentence on their own, and gives rewrites that properly incorporate them into sentences. The document aims to help improve writing by identifying and correcting these common grammatical errors.