1. Invite 23 people (including you). This is the number needed for a more than 50 per cent chance that two will share a birthday (assuming random selection of guests, which this won't be, but never mind, it's a party not a mathematical proof - though you could try to invite people who've never met).
2.Talk to everyone. Find as many coincidental things in common as possible, whether birthdays, ex-girl/boyfriends, pet dogs with same name, favourite Finnish delicacies (excluding vodka - too easy), weird experiences involving supermarket trolleys, whatever. The point is that coincidences can be anywhere, about anything.
When you find a coincidence, consider getting married, like the Huntrodds, if you are not already.
Work out the number of people needed to make a coincidence likely
3.Enjoy excuse to be nosy, or rabbit on about your past, while insisting that you are engaged in deeply purposeful exercise with potentially eureka results.
4.Award lavish prize to the best coincidence of the evening (assuming everyone tells the truth). Or a prize for the best invented coincidence of the evening. Or if your birthday is on September 19th, like the Huntrodds (and Jeremy Irons). Extra prize if you actually ARE Jeremy Irons.