Telling family stories is fun, and it's a great way to preserve family history. Or, if the story isn't true, it's fun for the campfire.
Start by choosing a funny or scary experience. If you don't have one, ask your mom and dad. Then work on memorizing it. Not word for word, but scene for scene. Things don't necessarily have to be in order, and facts aren't that important. Just remember the main parts. Were there so many frogs that everyone was stepping on them? A sudden attack by wasps?* Include it. Exaggerate it. The good thing about storytelling is that the family around you will jump in and correct your memory if you forget or misremember. (Bonus: this can lead to someone else telling a different story!) Finally, tell the story whenever you can. Around the campfire, in the car, at the dinner table - when things start to get boring, inject your story into the moment. Repetition breeds memory, and also breeds other people telling the story their way.
Try it. Tell the story often enough, and it becomes a legend.
* Real instances in one of my favorite family stories.