Here's a rule of thumb assuming that your audience is neutral about your topic. Only 10 per cent of your impact is in your content - 90 per cent is in how you deliver the content. Much of that 90 per cent is in your body language. if you ignore that, you're neglecting a fountain of natural, built-in credibility. Try this mental exercise:
Stage one: eyes
Imagine that you’re standing in front of your audience, looking around at them as you speak. At first, all you move is your eyes. Body and head are like a statue. Go on, try it… Do that to a real audience and I promise they wouldn't even buy a used idea from you. We don't trust people who don't move their head and body naturally as they speak.
Stage two: eyes and head
Keep your body still, but move your eyes and head together as you speak. This is higher credibility, it creates more trust, and it’s what most presenters do.
Now, do you want full credibility? Full authority? Full trust?
Stage three: eyes, head and body
Then move eyes, head and body together, even when sitting.
Watch any good presenter and you’ll see that when they turn towards part of the audience, their shoulders turn and their spine tilts in the direction of their gaze. The turn and tilt may be very slight, but it must be there.
Watch two colleagues talking casually in the office and the chances are you'll see both of them involving their entire upper bodies naturally, without even thinking about it. It's the pressure of speaking in the spotlight that makes us clamp down on these natural signals.