When you are freestyling, move your topic around. There is no topic. No stories or narratives, no straight lines. If you notice yourself starting to tell a story, jump to something else. Go perpendicular, switch to a different idea, say the first other thing that comes into your head using homonyms/homophones (words that sound the same but have different meanings: “flower/flour”), alliteration (repeated sounds: “pickled peppers”) and free association, even if just it’s some nonsense.
The point is to flow freely between and through words, sounds and ideas. Learn to do this well and you’ll never get stuck in thoughts and words. You’ll flow from one idea to the next. Some people like to tell stories and narratives when they freestyle. They can be really interesting and give you material, but when you reach the limit of the story, you can lose your flow, and then scramble to get a new idea out. With this practice you can avoid these moments or be ready for them. It doesn’t matter what you thought you were trying to say, what matters is the flow while you reveal new ideas and surprise yourself and your listeners.