The last story you should write is the most important story. You should start with a story that is just an amusing, entertaining, fun story to write and learn your writing chops with the least important things before you start applying them to the most important things.
Chuck PalahniukAs a child of the 1970s, I couldn't hold a narrative in my head; I was lucky if I could hold a joke in my head, because every time you turn on television or radio, it wipes the slate clean - at least in my case. After I gave up television, I found I could carry longer and longer stories or ideas in my head and put them together until I was carrying an entire short story. That's pretty much when I started writing.
Chuck Palahniuk