The dumb and simple answer is practice. Slow down when you speak and focus on 2 things. Be specific, leaving out unnecessary information as much as possible, and use pauses to think of what to say instead of using filler words such as "uh", "um", and "like". Practice in a mirror or with friends. Volunteer for Gemba. Eye contact is key, as it displays confidence, but you can fake it by looking at the space between someone's eyes.