what awesom-o said, plus:
RELAX.
i've given a lot of public presentations, both small and large, and i feel i've gotten pretty damn good at it. my trick is imagining that i'm at the bar, telling a story -- even if the story is boring shit about directx 12 -- and i try to structure my talk as a narrative, with three acts: one to (hopefully humorously) discuss a problem or assess a common situation; one to walk the challenges of this new tech or approach; and one to go over the opportunities and possibilities. having one or two good, relevant stories that you can drop in a couple minutes ready at hand helps.
also acting lessons helped me tons. kinda late for that, but if you plan on doing public presos again, learning how to use body language and physically engage the audience

helps tremendously, and makes the difference between SNORE and OMG MOAR PLS