Practice, practice, practice... in front of classes; but, sometimes it never goes away, you just get used to presenting anyway. In a doctoral class I was in once a quiet fellow was presenting. He started by telling everyone that he would rather be doing just about anything rather than standing in front of everyrone, what he was doing now... he and everyone giggled and laughed because we all could identify. No one thought any less of him and he became very charming and well-liked. Dont worry about it... we have all been there.