Yeah, uhs kinda suck. Force yourself to be silent on the uhs. Works great and really sounds like a dramatic pause.
My worst fear is not getting a reaction out of the crowd so I tend to blanket the speaking with some humor here and there. Sometimes it works...sometimes it doesn't.
Helps to know what you're talking about...and you do....and that really comes accross no matter what.
Going over the "show" full voice in a mirror or just walking around the house really works....never sit.
Edit: OK, you can go over it full voice while you are driving and I suppose that's sitting. lol