Haven't flown BA for some time, but I reckon Virgin could rival you for the length, frequency and irrelevence of Cabin Crew PA's! Jeez, they do go on and on and on and on......
Keep flight deck PA's brief (please...!). Always sound like you know what you're doing, and you know what's going on outside the aircraft, especially when you're delayed. Never refer to anything safety-related by any kind of emotional or loaded terminology that you understand, but the average pax doesn't. Don't do a cruise PA if there's a moving map display in the IFE; you only reduce your passengers' confidence in you if there's the slightest discrepency between what you say and what the IFE says; for instance, have you checked where the IFE's 'time to destination' was based on - destination or diversion? Often it's the latter ('cos it's based on your FMS/FMGS flight plan), and therefore it may be very different from what you say on the PA. In any case, why tell me what I know already - interrupting my movie/meal/sleep while you do so?
Do tell me in the descent what time we're going to arrive, and be honest about any delays. Update me if the delays get extended or cancelled. Don't go into too much detail about the weather; I know you've got a detailed TAF and actual, you don't have to prove it.
Don't welcome me to XXX on the ground unless it's your home base, but do tell those selfish barstewards to sit down and stay strapped in until the lights are off - and mean it!