Using confident body language greatly increases the chances that someone will like you. And you will start a sort of positive feedback that helps you improve your feelings. If you do it long enough, you will become the person your body language is projecting! It is completely true, believe me.
It goes like this: if you smile, people assume you are happy, no matter how you feel. So if you act confident, walking the walk, standing tall, hands relaxed, most of your weight on one leg, looking people in the eye, relaxed shoulders, and a lower tone to your voice, people will think you are confident, because that is how confident people behave.
It does not matter what you are feeling inside. All people see is your cool, calm exterior, and so that is the way they react to you. And as people react well to you, that improves how you feel about yourself. And before you know it, it becomes the way you are.
All the best,
Chris