Pronounce Words Correctly
Increase your brain power by studying how words are pronounced correctly. There are some words that are difficult to pronounce, so in order to speak intelligently, study how to pronounce these words.
You can also enroll in a speech class and become a more intelligent speaker if you show interest in what the other person is saying. One of the ways you can increase your brain power is to ask questions. People appreciate it when what they say is appreciated, and you can show appreciation through questions.
Lastly, believe in yourself. The only way to speak more intelligently is when you know your strengths and limitations.