Record yourself speaking. Find a paragraph in a book or newspaper you are reading, and speak as naturally as possible into some recording device. You can do this on your smart phone.
Watch yourself speak. Do this by standing in front of a mirror while reading a text. Watch your face carefully, paying attention to how your mouth moves and your facial expressions. Which facial expressions are friendly? What are not friendly? Also look at your body language. Leaning in towards the audience shows enthusiasm and good eye contact shows confidence.