More than learning public speaking, I would suggest finding ways to communicate your passion for the subject you will teach. This can be practiced as a mentor. Nearly anyone can learn to be a "talking head" at the front of a classroom, but it's a real art to inspire and to incite students to think critically. If we only present facts to the students, we can't be surprised when they aren't able to answer application level questions.
After I assign a reading assignment, I ask questions like "What do you think is the worst thing that could happen physically to a patient with ______(ex- CHF exacerbation) during a shift? What would you do if it happened? What would you do first? Which of these activities could you delegate?"
My class sessions are a dialogue, not at all a monologue. I spend very little time in straight "lecture" mode. Also, reading books on teaching can be helpful. Some good ones:
Joy of Teaching by Filene and Bain
Creative teaching strategies for the nurse educator by Herrman
Teaching strategies for nurse educators by DeYoung
Evaluating and testing in nursing education by Oermann and Gaberson
That's a start. Also, the NLN offers certification as a nurse educator once you have been a full-time educator for two or more years. There is a great list of references available for the test, and there are many great books on this list that will help as you start your career. Here's a link.