Use breathing techniques so that your physiology works with you, rather than against you. Breathing wrongly will only make anxiety worse.
Don’t worry about pleasing everyone
There will always be people who don’t like what you’re saying but you’re not doing it for them. Focus on the people you know your message will benefit.
Think about the bigger picture
Imagine your life as a big canvas. Every speaking gig you do is just a fleck of paint in a bigger picture. In time, any mistakes you once fret over will fade into obscurity.
When you start having thoughts like “I shouldn’t be here” use reaffirming language and be assertive about it. Speak supportively to yourself both internally and externally.
Face your fears
What’s the worst thing that could happen while you’re up there? Thinking about this not only makes you realise you can cope with it but also that many of your fears are unfounded.