What is the secret of being an expert? The official answer is that you're an expert if you've been held up as an expert by field consensus, so if other people say that you're an expert then you are one. It usually relates to time in the field and to weight and variety of experience within that field.
Experts, however, don't necessarily provide the best presentations. They are wonderful at their job, but they can't always tell people about them. I have worked with a number of experts; all of whom wanted to be the presenter they are in their own heads. They want to be slick, hard hitting and entertaining. The problem is they are experts in being experts not in presentation.
So what are the 5 basic things that you need to do to present well?
You wrote the presentation, but have you actually read it out in one go? With the slides? We often find ourselves reading as we go, that's not good enough. You need to practice it at least twice... At least.
2) Put your notes down.
It may feel better with a sheaf of papers in your hands but it distracts you. You'll find that working without notes (you've practised it you see) will free you up to move. It also means that you won't talk into your notes.
3) Look up.
Eye contact is massively powerful, even for a moment. It gives the audience the sense that you are focusing your attention on them, it's slightly flirty and it gives the impression you're the dominant person in the room. If you have a problem with eye contact you can get round this by looking at the bridge of the nose, from a distance this looks very similar.
4) Don't worry what's behind you.
You can see the slides in front of you... why are you turning round to look at a bigger version on the screen behind you?
5) Talk normally.
There is a strange strangled 'don't like presenting' voice that lots of people use. It's a head voice rather than a voice that comes from the diaphragm. Try to relax and sound as if you're talking to people and not an audience.