Wrting columns is fun. All you need is a subject, and off you go!
But there you have its main difficulty, too. Because finding a good subject is easier said than done. The trick is to find a topic that has the potential of producing a few hundred words of serious thought, in a light tone; or a humorous event; or even just a simple occurrence that may be turned into an interesting story.
Once that problem is out of the way all you need is to obey the rules of story telling and to make sure it has a beginning, a middle and an end.
So, go on! Take to the streets and look for all the topics that lie about: people in the park, an unusual performance in the theatre or concert hall, a train ride.
And there you have it. Job done!