Recently, me and a bunch of my friends have made two notes on our phones: a Regrets List and a Things I Did Good List.
In both cases, the aim is to jot down a note each time we do a small thing that 1) we either regret or are happy about, with 2) a distinguishable pattern / possible lesson to take away from it.
In my case, some of the regrets are:
spent $50 on drinks I didn't want
scheduled an unnecessary call in the middle of the day
ordered a salad without saying "hold the dressing" and got dressing soup
The items have to be small and have a fairly clear takeaway, and relate to something recurring in your life – this is not the place for big-picture life reflections.
Since you accidentally re-read the list each time you add to it, you slowly start to internalise small personal life-lessons about which kinds of decisions you most consistently end up regretting or appreciating.
It's especially useful for training yourself around decisions that get made quickly, like ordering at restaurants: I have had uncountably many experiences of ordering over-dressed salads, but without the Regrets List I would never sufficiently internalise that lesson for it to be top of my mind at the moment I order.
Of course, the Things I Did Good List has the added benefit of reminding you that you are, in fact, doing good. (Is it telling that our language has no one-word positive equivalent to the word "regret"?). Slowly you can watch items migrate from your regrets list to your Good Things list, as you make good decisions in the moments you would previously have made bad ones, and you can feel the system work.