If you aren't confident, gaining confidence is pretty difficult to do, but t's essential, especially because of talking in language lessons, and getting marked on it for English. Even if you don't feel confident inside, it's always best to look as if you are, and not do what I did in front of 100 people last year and literally squeak one sentence out lol. The secret of being confident is the way you act towards others. Stand tall and don't act scared, just nonchalent. Remember that if it's a speech or something, other people have to go through the same thing as you which isn't so bad! If it's just walking down the street just think to yourself, 'If they find fault with me I don't care. I'm happy with myself and I can find a hundred things wrong with them if I need to,' It sounds corny, but it should help you feel much brighter!
You shouldn't be afraid to look people in the eye, and talk to them straight. Don't keep looking down! Also, try not to make any unecessary movements etc. that will make you look awkward and scared :)