When you are freestyling, tell a story. Follow one topic or one narrative. Tangents are good as long as they fit together. Stay on topic until you finish your story or idea.
The point is to actually communicate an idea while you are freestyling without getting distracted. Some people have a hard time doing this. They jump all over the place, or just repeat the same idea over and over. This is about building a more complex idea through story. The story can be anything: what you did last summer, what you did today, a book you read, something from history. Tell the story in a linear way so it has a beginning, a middle and an end, and you will hook an audience that will hang on every word you say.
You don’t have to be a slave to the story. You can use poetic license to embellish the story and more importantly to keep the flow. Also watch out, a narrative can have a slow spot or reach the end too soon, and you’ll get stuck and drop your flow. So make sure you also practice the complementary “Free Freestyle Style” (p??) technique to help you switch over once your narrative is finished.
You can use the theme or element of your story to create a chorus during your freestyle. Come back again to the same chorus again during the story. This will tie your freestyle story together.