When i give a presentation i usually stutter on the first word so if i know that i am gonna block on a certain word either i skip the first letter of the word or skip the word entirely. And after i got that out of the way i can speak fluently the entire presentation just fine. Another thing that helps me is i usually speak q sentance as it were one long word and do not leave any gaps between the world. Try practicing in front of the mirror. Also write synonyms of the word that you u think you will struggle with that way if you block you can just say the synonym. I hope this helps you.