Yeah being calm definitely helps a lot, but I think the main issue here is self confidence. You mentioned that you would get really uncomfortable before you spoke, that’s going to make it really hard. A lot of people just say “be more self confident!” Which doesn’t really help a lot because that’s really vague. From what I have found is that the best way to build your confidence is to make promises to yourself and keep them. They can be as simple as waking up at a certain time, making sure you brush your teeth every day. When you start to follow through with these you will start to trust yourself more, which in essence, is self confidence. If you have a hard time talking to strangers just practicing any time you go somewhere public. Work on eye contact first, then talk to people who work somewhere and ask them questions about products etc. Its hard in the beginning but it definitely gets easier, it’s not as scary as what you make it in your head. I know because I have done it before