It's perfectly normal to feel nervous about public speaking, just as it's normal to feel nervous before an exam or an interview or a driving test. The thing to do is to try to set those feeling aside and try not to let them take over.
Ease yourself in by saying something bland: 'Good morning. Thank you all for coming. I'll take questions at the end, and I'll be around at the break if anyone wants to chat.' That gives you a chance to get used to the sound of your own voice, and judge if the pitch and pace is OK.
Aim to project your voice to speak to the people at the back of the room.
As pp said, don't speak too fast. Don't be afraid to pause, especially when you've just made a significant point. It gives your audience a chance to assimilate what you've said, and catch up on their note taking, if they're taking notes.
Don't have your hair flopping forward over your face. If that's your usual style, tie it or clip it back.
Don't look down at your notes all the time. Do the searchlight thing, where you glance down at your notes, then look round at different parts of the audience.
And if you're using Powerpoint or some other tech, have your notes with you on paper or on your own tablet too, so you can carry on if anything goes wrong. I've been to talks where the speaker has been completely thrown when the tech provided by the venue hasn't worked.
Good luck!