How can I stay more calm when I talk in front of people? ?

I get really nervous whenever I need to talk in front of big groups of people. Like to answer during class, talk during debate class, or make a speech. i always feel light headed and shake. My heart pounds really fast, my breathing speeds up, and I start sweating. This causes me to stutter when i speak. how can i change this?
How can I stay more calm when I talk in front of people? ?
Spot one person in the Group that you are talking to. Pick someone who looks like they would be really nice and talk only to this person. Tell yourself that this person will accept whatever you say because they are always on your side. No one else matters. This will help you stay more calm because you have someone on your side.
How can I stay more calm when I talk in front of people? ?
Just imagine yourself as very tall and they are tiny. That might help your mind believe you aren't afraid.