The secret to successful public speaking is to have a good time.  That’s the zen insight into the performance art that is presentation giving.  Of course, you have to do your homework, write a good speech, rehearse it effectively, and so on, but once you’re finally standing in front of that audience ready to share your passion with them, make it fun.  Let go of your technical worries, your insecurities, and your concerns about whether or not the audience will love you.  Have a good time.

If you have fun, the audience can too.  Everyone relaxes and the interaction between audience and speaker flows. 

A public communication doesn’t happen unless the audience gets it.  It’s not enough for you just to speak; the audience has to hear you.  And they will hear you most effectively if they can see that you’re OK, in charge, and having fun.  If they are worried about your mental state, they won’t be able to hear you as clearly.

So when it comes down to it, remember that the audience wants you to succeed.  Have a blast.