how do I overcome nervousness

Be prepared

If you have a presentation then study your notes and what you are about to say carefully before stepping up on stage. If you have an important meeting, do your homework so you know what will or may come up in meeting.

Doing this carefully and meticulously can remove a lot of nervousness. It may not always be fun. But being well prepared can be helpful not only to remove nervousness but also to ace the presentation or get the job.

Practice

The more you practise, take action and put yourself in situations that may make you nervous the more confident you become. You have been there before; you know pretty much what will happen. So you feel more and more comfortable and less nervous.