How do I do something more useful the next time lucid dreaming happens?

If you are really lucid dreaming, then you need to alter the fabric of the dream to one of your choosing.

I would suggest going somewhere where you can look at something to see how it's situated.  Then the next day, going to see if you're correct.  If you're correct in what you saw in the dream, great, keep that set of feelings and movements when you dream.  If not, try again.  Just pick a setting somewhere that won't change before you see it the next day, but of which you are not physically aware of it's arrangement when you are dreaming.  This is verification, and it can be something really small, as you said - the position of a pencil someplace you can check on it the next day, for example.