I was told this so much growing up but I still find it almost impossible to do in practice! I naturally have a lot to say and get very excited when I talk, so even when I'm fluent, it comes out in such a jumble that people have to ask me to repeat myself. I have noticed that I do sound remarkably calm, slow in pace, and fluent when I am explaining things to people in distress (like when I recently worked in an emergency room). Maybe I just need to pretend that everyone is in distress all the time.