I'm currently trying to design a plot for my campaign. However, I'm having difficulty finding a good system for developing the overarching plot.

I think it was from the YouTube Channel "How to be a great GM" that I heard of a 4 step process to go by, in terms of what the Big Bad was trying to do: Get something, build it up, test it, and then use it. Conceptually I like this, as it's a sort of build up and feels "organic" and human in a sense.

What do you use for creating your plots?

Edit: I've realized when I say "Plot", I less mean the plot of the campaign, and moreso the intentions and motivations of the BBEG, as that is the "driving force" of the campaign, in a large sense.