I have had to do a lot of public speaking in various professional and private capacities over the years. If I have done the work beforehand, then I really enjoy the experience; if I haven't, then not so much. I have always cleaved to the following (military) "mantras" to ensure the best chance of everything going well:
1. PPPPPP: Proper Preparation Prevents P**s-Poor Performance. (Speaks for itself)
2. Stand Up, Speak Up, and Shut Up. This works on two levels. The literal one: ie don't slouch; make sure you can be heard; and stop when you get to the end of what you have to say. On a more subtle level, it reminds me to (stand up) convey the impression that I am master of my subject, and am confident in my ability; (speak up) speak slowly and clearly, with due emphasis, in language that is appropriate to the audience and occasion; and (shut up) quit while I'm ahead, and still have people's attention. Listeners will forgive poor speakers most things - apart from droning on....and on...interminably.