This is an exercise which may be placed under the umbrella of meditative techniques.
At the end of day work backwards in "imaginative pictures" of your experiences throughout the day, last to first. Do this from bedtime back to the moment of awakening. This can greatly effect one's focus and strengthens thought; the more detailed the better.
Usually at first try one can be moderately successful but it becomes more difficult upon further attempts as the thought world is not so organized as one would like. Many thoughts can and will interfere, which is common to all meditative practices. Also if you fall asleep in the middle of the exercise then upon awakening it is best to return to the point of sleep and finish. This is aphoristic and calls for a more knowledgeable understanding but it certainly can't hurt to do so.
I forgot the name of this in German but something like "rukshaw" and so if any German speaking peoples, a correction would be appreciated. It probably means "thinking backwards".