There are 3 bits of advice on public speaking that persist despite many experts’ efforts to kill them.  Let me try to drive a stake through their evil hearts now. 

First, rehearsing in front of a mirror.  Let me say at once, rehearsal is good.  More rehearsal is better.  But rehearsing in front of a mirror makes most people self conscious.  They get more awkward rather than less.  Some seasoned professionals can do it, because they’ve already had a lot of experience studying themselves, and they can handle the self-knowledge.  But not the average speaker. 

So, instead, rehearse in front of an audience.  I know, they can be hard to gather.  But you’d be surprised what a good test rehearsing in front of a child is.  If you can keep an 8-year-old’s attention, you can usually hold an audience of grown-ups.   So round up a child or children and go to work.  Failing children, a dog or cat can be a second-best option.  Really.  The point is to have something animate besides yourself to talk to. 

Watching someone talk to a child is interesting.  Some people dumb it down, talking like the child is an idiot.   But most people just loosen up, get more lively and expressive, and show a lot more energy, all in an effort to make it interesting for the short of stature and attention span.  These are good things for speakers to do. 

Second, beginning with a joke to set the audience at ease.  This bit of advice is a recipe for disaster.  Most people are at their most nervous at the beginning of a speech.  To start with a joke, which requires delivering a punch line with aplomb, simply ups the ante and makes it even harder to succeed.  Don’t do it.  Start with a relevant story that frames your talk intriguingly. 

Third, "tell ’em what you’re going to say, say it, and tell ’em what you said."  That advice came from the Army in World War II.  Don’t take it now.  We’ve moved beyond the day when we could tolerate so much repetition.  Today, we’re on our Blackberries if we sense that the speaker is just running over an agenda or telling us what he’s going to say.  We only want and need to hear it once. 

So there it is:  don’t rehearse in front of a mirror.  Don’t begin with a joke.  And don’t say everything three times. Please.  Please.  Please.