We’re all a blank canvas of potential until we need to make an impression. There’s no middle ground in confidence - only extremes in the wrong direction. You’re either confident or not - push any further into either direction and you become arrogant or a recluse (or both; a compulsive YouTube commenter). But there are no/few commercially successful people who don’t give off a confident impression. No one wants to do business with someone who is unsure of themselves, and no one wants to listen to someone who can’t figure out if what they’re saying is right or not.
It’s not a secret that people make their first judgements of someone within the first few seconds. Conscious or not, the assumptions made about you early on will linger like school reputation at reunion day. Regardless of your experience, expertise or even knowledge - if you can’t convince your audience you’re not afraid of them (in a presentation or on camera) in the first few seconds, the next couple of minutes will be a case of clawing back confidence from the people who are hanging on your every word.
I’ve performed stand up comedy for a few years now in Asia and the UK, and I maintain that a first impression will always come sooner than you’re ready for it. From the point where you pick up the microphone, or even how you enter the stage, every element of your physique, your walk, your style, your facial expression - the list goes on - is analysed, broken down and reconstructed in the shape of how confident you appear to be to everyone watching what you’re doing. On stage it's a case of walking out like you're walking into your own room (minus the desire to fling your shoes off or sing into a hairbrush etc). Owning the stage, like everyone else is there because you let them. Personally I would try to seem cavalier about it - almost like I could take it or leave it - grabbing the microphone stand aggressively like I didn't care if it fell over. The last sentence, of course, doesn't quite apply in the corporate environment, but the philosophy is true to both scenarios. In all cases, owning the stage is essential. If you don’t believe you belong there, neither will anyone else.
There’s a lot of tell-tale signs when someone is unsure of themselves, and it’s because of how conscious you become of yourself. This is especially true when making a presentation where every movement you've ever taken for granted feels like it’s the most animated you’ve ever been, like lifting your finger will set off the bells in Notre Dame. The most common confusion comes from people’s arms - what are you supposed to do with them? Nothing’s weirder than someone talking at you for 20 minutes who keeps their hands straight and stuck to their sides like their having a nativity play flashback, and you can’t fold them or you’ll look like you’ve being told you aren’t allowed any more biscuits by your mother. Since you’re on stage, larger movements don’t look as big as they feel, so put emphasis into you words with your hands. That’s not to say cartwheels and cheerleading choreography will help you out, but follow Steve Jobs’ example - busying his hands (conveniently holding something, usually), and pacing where appropriate. Being aware of your space and using it can make you feel - along with the audience - that the stage is yours. Just try not to look at your feet as much as Jobs did; it’ll either make you look like you’ve forgotten what you’re saying or that you’ve put your shoes on the wrong feet. It’ll be very tempting to look at one space and focus on it; I would advise to constantly redirect your attention but to nobody in particular. A light in the room, someone’s bag, anything that won’t give you awkward eye-contact (unless the context calls for it) but will let everyone assume you’re just looking at somebody else.
On camera it’s the opposite problem - your movements are exaggerated to the nth degree and your eyes will usually say more about you than the rest of you put together. As bizarrely unnatural as it feels, focusing in one place wields a more confident look than wandering eyes. While in front of a live audience it looks more natural to redirect your attention regularly - so to share the presentation with everyone - on camera everything is exaggerated so movement or wandering eyes might give the look of a nervous person, or perhaps a person surrounded by bats. So relax and find a focal point in the studio that isn’t the sound guy’s curry stain and stick with it.
From this point, if you’ve come out confidently, the rest should come naturally. Assuming what you’ve got to say matters, and the information comes across coherently (all of this was for nowt if you can’t talk over the air-conditioning), then you’re ready to paint that blank canvas of potential and prejudice whatever colours you want.