How to write a story arc like Greg Weisman

To put it simply, i want to do what Greg Weisman does; write a complex and compelling story arc with complex and compelling characters that all seems to add up once explained.

So, how do i do that?

I would simply suggest you start write an outline.

Perhaps show some friends the general idea. that kind of thing. It also largly depends on what kind of story you want to write.