Explain to your child that other people use profanity, whether you want them to or not. Then stress that your family doesn't believe in using bad language. Remind them that words can hurt, too. Explain that swear words often hurt people's feelings. Tell him or her that just as hitting or kicking can hurt people, words are equally effective weapons that can leave emotional bruises.
Image is everything.
Talk with your child about how people look at a kid using foul language. Explain that when kids swear, it makes people think badly of them and gives them a poor reputation. The most important thing you can do as a parent is praise them for doing the right thing. If bad language has become a problem and little Johnny actually catches himself and corrects himself before saying a bad word, be sure to tell him how proud you are of him. Positive reinforcement is the way to get more of the good behavior and less of the negative one.