Dependent clauses contain both a subject and a verb, but they cannot stand alone as sentences because they depend on an independent clause to complete their meaning. Dependent clauses usually begin with words such as after, because, before, if, since, though, unless, until, when, where, while, who, which, and that. You can usually combine dependent-clause fragments with a nearby independent clause.
If you cannot smoothly attach a dependent clause to a nearby independent clause, try deleting the opening subordinating word and turning the dependent clause into a sentence.