It’s not easy being funny. If you have time to warm up you can get better, your jokes become smarter and you come up with them faster.
Try write several ideas for the hashtag #FactsWithoutWikipedia. Write at least 3 and see how you improve as you warm to the subject matter.
Writing is like that. You don’t sit down and light the keyboard on fire with your great ideas. Start, then warm up and then you will find yourself in gear, roaring into the first lap of your writing race.