Do more presentations! It is easiest to start off in front of people you know and feel comfortable around. Volunteer to do presentations in front of those people. Once you are content with those presentations, move on to presenting in front of people you don't know. Practice, practice, practice before presenting in front of those people.

Try practices either infront of your friends.Also during presentation look at the audience forehead

First of all, to be more confident, people has to believe in themselves and has to have enough knowledge, skills, experience to deal with any situation. To have those condition, people has to learn and practice many times, and they also need to know themselves about their advantage to build up their confidence.

Secondly, they should practice by their own way, at the beginning could be alone, then with some closed friends/ colleagues to create a peaceful environment for them to reduce the stress and to practice/ to perform easier.