If you ever have the opportunity to speak in public it is highly probable that you prepare the event in advance. First by writing a script, or at least some notes so to be able to follow the story you wanted to tell. Then, some visual support in case it could be useful or to help the audience to follow your words. With that you expect to have the best possible speech because any good presentation, requires time, interest and attention. You don’t want to leave out any important thing, sharing what is key. So you script your speech, then search for some good images and data to accompany your words. Finally, you rehearse it again and again. It doesn’t guarantees that nothing will go wrong but it will help if any issue comes up.
The other way to face a speech is by starting the other way around, with the data and images and then building the speech. No visual as help or support but as the roadmap to follow. Your speech will adapt to whatever shows on the screen. Well, in that case you must be confident that you know all possible data, that you master the topic or at least you master acting. If anything goes wrong you will need a full set of skills to come out of it successfully.
But, you can also just leave everything to improvisation. Or maybe the situation itself leads to you a not possible to prepare situation. Then, rely on your knowledge and skills, they will be highly useful.
So any time you have the opportunity to prepare a speech, meeting, .. every time you need to say or not to say (to measure your words) use it. Write the script (agenda, main topics), the visuals (what you want to share, how do you want to dominate the scene and not let the scene dominates you), and your talk (rhythm, words, pronunciation).
And once in action, slow down. Moreover if you will not be using your mother tongue. It will give you time to think and react avoiding gaps, mistakes and later on self regrets.
Improvisation is not a good companionship when being in public. It doesn’t matter if it’s a company event, a meeting or a speech.