Staying cool
When giving a speech or making a presentation, be thorough with your preparation, make an outline of the points you want to touch upon, and prepare in advance for possible questions.
At social functions, learn to relax and be yourself. Don't be pretentious. Talk freely, as if to a friend. Only confronting such situations repeatedly will help you overcome your insecurities.
Reduce stress using meditation techniques which will keep you calm and relaxed.