There are many ways that a person can improve his or her communication skills. One great way is by going to a group or individual speaking class. Classes can help a person become more comfortable speaking in front of an audience, overcoming fear, and much more.
If you have a large vocabulary, the odds are that you use it in everyday conversations. It's not uncommon to hear someone say they don't know how to pronounce something because they don't speak a lot of the language in question. A large vocabulary and variety of native languages have great advantages when talking to other people.