Every day write down at least one idea.
This might take many forms, it might be an blog, a notebook, you can do it on your Palm, or maybe you can write on the real palm of your hand. It isn’t even so important that your annotations survive more than a month.
Nietzsche did it, so why can’t you? He had lots of messy notebooks, particularly at the end. But i digress.
Most people have blurry notions about life. You walk around, you see the world around you, and you have opinions. Sometimes you laugh about someone’s way of answering a question, sometimes you wonder about how such and such clothes usually go together with such and such moods on the persons. Sometimes you even wonder what it all means!
The exercise is exactly to pick those indistinct musings and put them into words. Sound-bites, if you can. And write them down, to show to yourself.
But do not have a fixed time of the day for it, do not force yourself to have a witty thought. Just stay alert for the moments when your head thinks curious and interesting thoughts.
At first, write down even gibberish.
The catch is: after some time, having put them down, you begin to review your own ideas. Some of them you reuse. Some of them you rephrase. Some of them grow more and more important. Some fade. But having writ en them down, you allow yourself to expand your repertoire.
Depending of how well you do it, you might find that you get used to the thing and start writing more than one idea per day. And this is good.