Most of us can write one story.
The best place to start is a story about you. Some event or point in time in your own life and how it shaped you. Most of us wish we had a diary, old letters for anything writing from an ancestor that we might know them better. Your family will know doubt feel the same.
One memory of an ancestor…perhaps your parent or grandparent? Were you lucky enough to have known a Great-grandparent? Write down your memory or memories of them. What where the story occurred, what was going on? What were the sights, sounds, smells, textures, etc. in that memory?
Those of us with children wish in retrospect we had written down – all the things they said, their joys and sorrows. This may be the time to write down those that you remember. Perhaps, you can write down the stories of your grandchildren, knowing their parents may not have the time to write them down.