This one's an easy one, folks, and if it isn't an easy one, go find your third grade teacher and tell her (or him, but really, statistically speaking, it's probably a her) that they failed to teach you a very basic and necessary skill. It's simple: every sentence needs a subject (who or what the sentence is about) and a predicate or verb (what the subject does or is.) If your sentence does not have these two elements, it is, in fact, not a sentence. Poor little guy, he thought he was a sentence, but you failed him by not checking to make sure he has everything he needs. Do you want to be sending unsentences out into the world, unprepared and unable to meet the needs of the paragraphs and essays they are part of? All the real sentences will make fun of your unsentence, and your unsentence will have esteem issues...honestly it will be a big mess. A mess that could have all been avoided had you simply made sure that you did what your third grade teacher taught you to and checked that you had a subject and a verb. If your third grade teacher wasn't as great as Mrs. Smith, who was my third grade teacher, there are some sites below to help you practice.
A grammar rocks video about subjects and predicates
Subject and predicate practice game
A very complete PPT tutorial on subject/verb
