Couple of comments from one who listens to the PAs, and has to do quite a bit of stuff to audiences elsewhere.
1. If you find you tend to hesitate in mid-flow, write the key points down so they are in front of you, in order. This can help to keep going. We hope that the commander is up front because they know what all the knobs do on the flight deck, rather than being in a public speaking examination trying to do it without notes.
2. Do not be put off by the IFE moaners who don't want any PA to interrupt their beloved films. They are a minority. If there's something interesting under the port side, please say so mid-flight. And no need for a long apology "for disturbing".
3. If you can do even a one-liner greeting in the language of the destination country, please do so, it's appreciated, as long as your pronunciation of it doesn't give rise to laughter.
4. Do maintain professionalism, and avoid that terrible introduction "Ladies and Gentlemen, Boys and Girls".
5. Destination weather and even approach direction are always welcome, although not the complete arrival ATIS ! I've never heard the identification letter read out yet, but it's been close sometimes.
6. "I am your captain, John Smith" is better than "This is Captain Smith".
7. If you have to break off to deal with something, just stop, mid-word if necessary.
8. Don't pretend that touchdown at scheduled arrival time is "on time". Time is measured chocks-on at the gate, EVEN for the pax.
9. Finally, confident voice. Speak clearly into the mike, don't mumble, not too fast. And smile as you are saying it (this really works).