I've found that just being completely forthright with the passengers, but yet not being monotone and dull usually pleases the great majority. Sure, some want more, others want no PAs at all, so falling in between usually works out well. I think the only thing that is missing from all PAs across the board is total honesty.
I also don't apologize for things outside our control. If we are diverting for weather, or if there is a huge delay for takeoff, I don't apologize. There is nothing we can do, so I just say "We plan to have a 30 to 40 minute delay from leaving the gate until we are airborne" without the "sorry."
Jumpseating home one time on a major airline, the crew came on the PA and said to the passengers, "We might experience a few bumps ahead since we're deviating around some rain showers, so we recommend you stay in your seats since the seatbelt sign is on." Well, we got hammered at one point deviating, with some pretty rough bumps. The guy next to me goes, "Glad they recommended we sit down" with a grin. So from now on, I've learned to say, "Ladies and gentlemen, the seat belt sign is back on and we require you all to stay in your seats with your seat belt fastened until we clear some storms we are deviating around." Makes it pretty clear.