In my public speaking training session, there is a segment what we called "Persona Interview". In this segment, a participant will step forward and take a role of a persona that he/she doesn't resonate with.
For example, once there was one guy (Let's call him "A") in my training session who took the challenge and put up a persona of a "professional bodybuilder", even though he admitted he didn't look like one(we could see that too!) and it had been ages since he went to the gym! As he sat in front, anyone in the room can throw him questions. He would then have to answer those question, as if he was an expert in that field. The only rule we used in the game was that, whatever, this "bodybuilder" answered (even if we knew it didn't make any sense), we would agree with the answers because afterall he's a "professional bodybuilder"!
Once the segment kicked off, we had a good laugh because we received all sorts of funny answers. And because we sticked to the rule, we accepted all answers and asked even more questions - getting more funnier answers.
As the segment progressed , "A" grew in confidence answering those questions. Why was that so?
"A" mentioned that one of the main reasons he felt confident because he knew that he would not be faulted for any of his answers. That took one major "burden" off his mind.
You see, we are too judgmental even on ourselves. That doesn't make us look confident when are presenting. We just need to kick that habit out. Why judge ourselves, even before we step out to speak?
If "A" could be so confident answering the questions, even though he was not a "professional bodybuilder", we can definitely be more confident speaking in our professional/ personal capacity - given that we have all the content with us!
So, if you would like to achieve that confidence level when speaking in the public, why try this activity as you are rehearsing for your presentation. Put yourself in a persona, and rehearse your presentation in that manner. And see for yourself what difference it could make.