Preparing to be a columnist these days involves always recording and observing current affairs, or noting your own state of mind about the events. It requires imagination and personal industry to come up with ideas on a consistent basis, as well as the reflection and perceptiveness combine life experience with those original thoughts. Being curious is also an important trait -- you should keep informing yourself about your area of expertise if you are writing columns on specific matters.
A writer who is going to frequently cover a particular topic also keeps a current file of the news articles available for reference material. A columnist also prepares by developing sources (people, archives, and other resources) that can be tapped for expert or key inside information or ideas. Whatever type of column you are doing, you need to be able to talk to a lot of people who will divulge the information that you can incorporate into your columns. Always be ready to use the prominence gained from your status as a writer (or the intriguing nature of the subject matter of your columns) to gain interesting new data from a targeted group of friends and industry persons insiders.
A writer should prepare to make a point in a way that the masses will understand, since your communication skills will dictate how many people actually come back to read your column again and again. Whatever the topic being written on, it must be simple enough for regular readers to grasp, and brief enough for them to maintain interest until they are finished reading through all of it. Syndicated political columnist George Will, for example, once advised if you can't get it plainly said in 700 words, you just don't know how to say it.
Ensure you have a system in place to check the accuracy of your piece, be it the editor, or through a habit of writing that builds the accuracy and fair-mindedness into the structure of the column. If these precautions and preparations are consistently maintained, you could have little problems staying organized to consistently put out your columns.