I have the same problem, so I don't know how much I can help, lol. As someone suggested to me, and as I have tried before on different things,have a script or a guide to help you say what you want, that can help lessen the seeming nervousness at first before you warm up. If I write a script I always end up going off course anyway, so that's why I mentioned a guide, lol.
Another thing is to just keep doing the same video until you feel like your delivery is better. I did at least 10 or more takes on my channel trailer before I gave up and just posted it because it was better than my previous trials

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The best thing for me so far is just posting videos with commentary. At first my videos where pretty robotic sounding and didn't have much personality, but since I've posted so many where I just play and talk at the same time, I've gotten used to the idea that random people on the internet are going to hear me talk, and I'm a lot more comfortable with it. I'm far from the smoothest talker, and still learning how to best "create" my youtube personality, or really just show my personality in my videos other than when I'm doing commentary (the beginnings of my videos still sound robotic, for example) but the more I do it the more natural it feels.