Start learning as early as possible. If you're reading this while in junior high or high school, you can start preparing now. Look for extracurricular courses dealing with computers, public speaking, communications, English, and foreign language.On an informal level, start familiarizing yourself with sports terminology and history. You should also watch and listen to popular, professional sports announcers. Observe their style and skills; take notes, so that you have a document to reference as you develop your own announcing style.