Preparation and practice.
If your company offers any training in it, do it.
I also recommend Toastmasters - there's a series of 10 prepared speeches you work through, each one focusing on a different aspect, so for example, my next one will be the 5th one, which looks at body language. Each session also has table topics, where you talk for about 2 minutes on an unprepared topic, which I find much harder, but I can see my improvement - I am more likely to pause than go er, um... (though I still have a good few of those.)
Even if you don't join a group, the website has quite a bit of useful information - some of the guides are available to non- members. If you install the app, I find the timer useful - you can use the set times, or do a custom one, and it changes colour. A prepared speech should be 5-7 minutes, so it goes green at 5 minutes, yellow at 6 and red at 7. I don't always speak at the same rate (nerves etc), and I am getting better at having sections which are less important which I can leave out - or add in, if I'm going too fast with nerves.
Depending on what you speak on, you might have a section at the end for questions from the audience, and it might be useful to have some etra information prepared in case they're not forthcoming, and you need to fill a bit of time.
Filming it is good, too, especially for the body language stuff - you become very aware of how you wring your hands or gently rock from side to side, or only look at the people on the left...
But whichever way you get there, it's basically knowing your material and practising. It does get easier with time!
If you have the opportunity, check out the room you'll be talking in, so you get an idea of the space. And if you are presenting with slides, have a backup on a USB stick, and be prepared to adapt to speaking without it, e.g. hard copy of notes. If anything is going to go wrong, it is most likely to be the techouse, especially if it is the sort of event with different speakers from different places.
Kept practising!
(Propanolol is what finally got me through my driving test, so it's worth considering!)