Have you ever heard the rule where you should never end a sentence with a preposition? Well, that's not quite true in all situations.
First off, what is a preposition? Basically, prepositions are words that express a relationship between a noun or pronoun with another word or element. They can describe the position of something, time when something occurs, or the way in which something is done.
Mignon Fogarty suggests in her book, Grammar Girl's Quick and Dirty Tips for Better Writing, to see if the meaning of the sentence changes if you take away the preposition. Fogarty's example is "cheer up." "He cheered" means he is either a fan or cheerleader and "he cheered up" means he became happier.