YouTube is your friend here... generally, practise, time your presentation, breathe and slow down your speaking, be prepared for the questions you might get, don't have too much detail on one slide, and don't be afraid to say you'll get back to people if you don't know the answer.
Lots of presenters use notes to help them, cue cards or index cards or similar.
Maybe watch a few TED talks on the topic as well, many are given by brilliant speakers.
You got the job so there must be something about you. I've seen a tendency recently to use stories a lot more than when I started in the workplace; depending on how long you're going to talk for you could have some activities.
I'm picking up that you might encounter a bit of resentment from those who didn't get the job, be courteous and smiley and use eye contact to incorporate as many of those in the audience as you can. Also keep your tone of voice neutral if possible.
Best of luck with it, I'm sure it will go fine.