There is probably no shortcut to that skill. Try to find speaking opportunities on topics you know about, e.g. at meetups. It is better to start in front of a s

There is probably no shortcut to that skill. Try to find speaking opportunities on topics you know about, e.g. at meetups. It is better to start in front of a smaller group (10 people), from my experience nervosity is lower when in front of a smaller group. Record your talk and listen to it afterwards in detail and find things you want to improve. Don't hesitate to ask for feedback from others, and don't take it too personel. Try to be objective like you would train for a sports challenge. Every public talk will improve your skillset a bit, so you need to just do it!