You’re asking the million dollar question. In short, it takes practice. What I will do is talk to my family and try to get myself to stutter, which isn’t hard. Since I know they don’t care, I can really zone in on what happens when I stutter. I notice that both my throat and diaphragm are tense. Really the best way you can combat the tightness is by breathing *a lot*. Try and take frequent short breaths while talking and see if it affects the fluency of your speech. While it’s not ideal for normal day-to-day conversations, it’s a good way to eliminate the tenseness and make yourself calmer in any situation.