Start with a subject. The subject of your sentence is the person or thing that the sentence is about. Any noun or pronoun can serve as the subject of your sentence. For instance, "The dog" could be the subject of your sentence.
Select a verb. The verb tells you what the subject of the sentence is doing. To ensure grammatical correctness, your verb must match your subject in number. For example, if the subject is singular, girl, the verb must be singular. If the subject is plural, the verb must be as well. If the subject of your sentences was the dog, "ate: could be your verb.
Include an object. The object of the sentence is the person or thing that is being acted upon. In the sentence "The dog ate," food could serve as the object.
Add a prepositional phrase. While a preposition phrase is not necessary to make a full sentence, adding one can increase the complexity of your sentence. A prepositional phrase tells readers when or where something is happening. Prepositional phrases consist of a preposition and an object of the preposition. For example, you could increase the complexity of the sentence "The dog ate food," by adding the prepositional phrase, "in the kitchen."
Combine elements with conjunctions. To make your simple sentence a more complex one, use a conjunction such as "and" or "but." You could, for example, say "The dog ate food in the kitchen before his master came home."
Spice up the sentence with adjectives and adverbs. Adjectives, which describe nouns, and adverbs, which describe verbs, add excitement to your sentence. You could spice up a sentence with the addition of these elements by saying something such as, "The unruly dog messily ate food in the spotless kitchen, before his master came home."