You know how to keep an ordinary diary; in the evening you write down all the incidents of the day, at the same time as you make considerations over them, evaluates them.
But to keep philosophical diary is not to keep such a retrospective diary, it is to write all thoughts - both positive and negative - down at the very moment as they arise.
Nor does it consist in trying to write profound and philosophical thoughts down.
The philosophical is lying in bringing a passive listening presence into the thoughtprocess.
The great philosophical thoughts will then begin to come by themselves.