At weddings as soon as the B&G indicate that they're ready for the first dance I grab the radio mic, go out onto the dance floor, welcome everyone to their evenings entertainment, tell them what's gonna happen over the next three songs, to get cameras ready, ask them if they've had a good day (I'll soon put an end to that) and then get them to give the B&G a big '5 Star' cheer as they come onto the floor.
After 1st dance prompt rest of bridal party and later persuade everyone else to get up for the 3rd (sometimes works, sometimes not).
I do have quite a large selection of jingles on minidisc and occasionally use them. I've also made up a few of my own using snippets from records. To give you an example. Last xmas to start the shows after the meal I made a jingle which started with 'Ladies & Gentlemen, boys & girls , it is my pleasure to introduce to you' (from Big Brovaz) then into some personal jingles. The whole thing lasted about 30 secs and gave me the chance to get from behind the decks out onto the dancefloor for some chat to wind the audience up ready for some serious partying.
Using minidisc for jingles is an easy and cheap way. I limit the number on each disc to about 100, only about 5% of the disc but it makes them easier to find. If you have nothing interesting to say between 2 records and they don't mix easily stick in a short jingle.
For birthday parties, if it's a surprise one I prime the audience that as soon as the individual arrives I will play 'Happy Bithday'. I've found if you don't organise this bit they'll all start at different times & it sounds awful. Then three cheers followed by the No1 record on the day that they were born (it brings a tear to the eye - especially if it's something like Clive Dunn, Grandad)
I think the important thing at any gathering like the ones we do is to try and break the ice (some weddings can be more like wakes). I don't tell jokes but might make a jovial/ light hearted comment related to the event or the venue - if you can get them laughing or cheering you've usually got them on side - how long that lasts is another matter

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PaulS