Basically, how do I write stories about my fortress, like Boatmurdered or Glazedcoast?
Just take small notes while your playing when something interesting happens. You might find that there isn't much to report about at first, but you just need to look a little closer at whats happening around your fortress. Who is friends with who? Anyone have a grudge? Do people worship any strange deities? Any strange wildlife roaming about? Any inexplicable injuries? Who's the most skilled dwarf in your fortress, and are they happy? Is anyone happy? Are they unhappy for a particularly gruesome/ridiculous reason? What room is covered in blood and why? What's your fortresses main export? What about your leaders, are they crazy, neurotic, or just sadistic? Have you made any mistakes during play that might be explained from the perspective of a dwarf ('the gods must be crazy' or 'this overseer is incompetent')? And so on. . .
Just the question, "why does this fortress exist?" and you might discover a really interesting story. Be prepared to stretch the literal gameplay into an interesting narrative - Dwarf Fortress remains a closed system where most every strange quirk or event is explicable. The wonder and magic of the story has to come from you!
And don't forget the ever-popular "What is Urist wearing?" ....I have had a (male) one-legged Championdorf who was partial to dyed silk shirts, and always wore one leather mitten. He was not missing the other hand, he just didn't want another mitten or glove. I made numerous gloves and mittens for the fort, and occasionally he'd wear out his one mitten, and replace it (I think he did replace it with a glove, I'm not sure), but never the one on the other side. Probably had something to do with crutch-use. But his personal clothing quirks were fascinating to me, and a lot of story could have evolved from his choices.
Then there's the enjoyment of watching an Artifact Mug that everyone wants to drink from do circuits around the fort....