Practise!
Athletes are practising 90% of the time. How much are you practising in your daily job?
When you speak in front of an audience, they are only affected by 7% of your words. The rest is voice and body language. Practise! Ask someone to listen to your presentation.
Try to take a short break while speaking. Change now and then your tone of voice and do not move around that much! Good Luck!
On the video clip I am about to start up a conference. I am alone in the room and have some time to practise. Not the very best rehearsal! But as it is said, the worse rehearsal the better performance!