How do you design your campaigns?

Let me define a campaign as an episodic story with a clear hook, rising action (or actions), climax, and ending. It would ideally be a story that goes for multiple (at least 4 or 5) play sessions so as to distinguish it from a one shot.

How do you, as a DM, develop and run these?

Over the years in my group we've all taken turns running campaigns, one shots, sessions, etc and what's always fascinated me most is how everyone's planning style is so different. Some get into ridiculous detail, while others (guilty...) tend to improv.