I used to practice a lot before my presentations and that definitely helps. I would stand in front of the mirror and record my presentation and play it back. I memorize what I have to say (so it feels like I'm "reciting" as opposed to talking) and when I block I'd think of an alternative way to say that sentence and memorize that too. If i find that theres a word i keep blocking in, I change it. I'd practice until I can have it come out in the most "natural" way I can. When I would get really stuck mid presentation and just can't get the sentence out I'd cough then keep going lol. For some reason it was like I clicked reset.