From the Atomic Robo blog, Brian Clevinger reveals part of his writing process:
Each story has three acts. Each chapter of that story has three acts. Each scene of each chapter has three acts. Each conversation of each scene of each chapter has three acts. In a sense, though at this magnification our definitions begin to blur, each line of dialog has three acts.
All you need is a set up, a conflict that follows from the set up, and a resolution that follows from the conflict. This’ll come naturally with practice. It might feel a little artificial to you, especially at first…
The precise end of a given act and the beginning of the next is less important than the fact that there is a set up, a conflict that arises from that set up, and a resolution that follows from that conflict.
And if you’re a Atomic Robo fanboy like myself, you might want to check out Brian’s breakdown of Atomic Robo Vol 5, Issue 1′s into three acts (for both scene and issue).