John Cleese offers some very good advice to anyone starting out as a writer -- steal from people you admire. He doesn't mean literally taking someone else's material and trying to profit from it, but learning how they do what they do, whether it's on the printed page, onscreen, or on the air. Be inspired enough to create your own take on the same subject, perhaps.
Cleese's suggestion isn't valid solely for comedians, but for anyone in show business at any level. My early interest in a radio career was sparked by listening to some of the best in the business, from whom I learned pacing, formatics, how to introduce an idea, and how to make it pay off. The same for my interviewing skills, which were sparked by watching hosts who displayed a genuine interest in what their guests were saying and the topics they were discussing, rather than simply reading a list of prepared questions with no regard for the answers.