Basic sentence structure consists of a subject and a verb. All sentences must express a complete idea. Anything less makes a sentence a fragment. Sometimes it can be easy to write in fragments. People often will write in fragments in order to get the words out in a hurry or to make a point. However, when writing for the academic audience or writing a more formal piece, fragmentary sentences are not appropriate and should be corrected.
Determine if the sentence has a subject. A subject is usually a noun that indicates a person, place, thing or idea. Example: The students went to the rally. Students is the subject.
Determine if the sentence has a main verb. This usually will be an action verb, but it can also be forms of the verb "to be" such as am, was and were. Example: The students went to the rally. Went is the verb.
Determine if the sentence expresses a complete thought. Example: Went to the rally. This does not express a complete thought because it does not tell who went to the rally. It needs a subject.
Determine if the fragment can be added on to the sentence before or after it as a dependent clause. Sometimes sentence fragments can be revised by making them part of another sentence by the addition of a comma. For instance, the fragment "Such as mountain bikes" can be added to the sentence, "He owned many pieces of sports equipment." Together it would read: He owned many pieces of sports equipment, such as mountain bikes.