rehearse it a lot. i know it sounds stupid and obvious but the more you can go into "automatic mode" the less you even have to worry about freaking out during the talk.

of course this is an OCD point of view

also whenever i have to give a presentation, i usually write down every word i plan to say, literally. not notes, like the actual speech. then i practice reading it out loud until it sounds like I am not reading but just talking. i don't usually end up reading the exact text but it's close, and it's comforting to know it's there and I can read it if I have to.

it's a lot of work to do that though. for me it's kind of necessary because i freeze up or get all garbled.