Start thinking about it now. The Government is going to want to know sometime soon, according to this report. To be more precise, the Office for National Statistics is to be tasked with including a Happiness Index in its periodic analyses of the nation's wellbeing. Details have yet to be worked out, but obviously there'll have to be some common baseline for the data gathering, and this can only start from the simple question: what makes you happy? Once they've compiled this universal happy-hit list, then they can get round to identifying the units of measurement (happicons?) and answering other awkward questions about frequency-of-happiness-arising-from, duration-of-said-happiness, conflict-between-simultaneous-happiness-sources - not to mention counterbalancing sources of the opposite to happiness, which is called unhappiness ... In short, all the usual kinds of things good statisticians take into account before they publish their findings. So it'll take them a while.
But hey, we have to start somewhere. So here's my random list of a few things that, more often than not, seem to make me happy. The right weather. Accidentally stumbling across something I'd completely forgotten I'd been looking for. The right music. Corny tearjerker moments in movies. Empty country roads. Smiles from strangers. Accidentally stumbling across something I definitely wasn't looking for. A problem solved by an insight. Oh, and of course, flashes of love, however brief.
Go, Office for National Statistics, start counting! We need your numbers, quickly. Otherwise, how are we to know how we really feel?