Have you tried reading premade campaigns? They can be a little pricey of course, but if you're just interested in how the plots and settings are constructed you could probably snag a campaign with good reviews written for 3.5 or 4e or Pathfinder for cheap. You can then get a sense of how they lay the groundwork for overarching events, how they set up NPCs with interesting motivations, etc.

If you're interested in DM advice that moves away from the "writing" paradigm and into a "responding to player actions in an interesting way" paradigm, you might also check out Dungeon World (or the original game it's based on, Apocalypse World, but that's written for a different type of setting obviously). Those are games meant to have the DM constantly make the player's lives interesting, rather than follow a pre-written plot - but some of what I've learned from them I feel is also applicable to making things interesting within the confines of a pre-developed narrative.