Look into Toastmasters. It is a successful community that is specifically designed so you improve this skill.
I have always been a very strong public speaker (loud, booming voice, native English speaker) and decided to do toastmasters to get better at talking about very technical things - I have ADD so I tend to fall over myself a lot when explaining things. I have had a very stressful last few months (organised a marketing conference, moved house, organised two gigs that didn't work out so well) and I was asked to present at a meetup a few days before the conference.
I felt really dizzy in the afternoon of giving the talk and thought a drink or two would settle me (the meetup was at a pub.) Turns out it didn't and 3 slides in I became very disorientated. I decided to professionally stop the talk and ask the MC if the next speaker could go first as I needed to get some air. I came back half an hour later and performed the talk.
The reason I was able to handle this so professionally was 100% due to Toastmasters. So many people in my club were not native English speakers who had very stressful reactions to public speaking. Every single person given a task would always show the upmost respect for those who struggled and act in a supportive manner, so when I had a rough time I knew how to act appropriately.