1. You’re first road is called your A-plot, and it is that part of your script which fuels the actions of the main characters in the script, and generally pushes the story along, as in: “Oh no, the city is under attack—thank goodness the Power Rangers are here to fight the monster and save us all!”
2. Your B-plot is that part of your script which expresses the emotional entanglements and problems of your main characters tangentially to the doomsday scenario that is unfolding, as in: Carrie Bradshaw’s life may be in ruins, but wait—who in the world is that dreamboat? Let me date him and report back to my friends!
3. Hour-long shows will usually also have a C-plot, which focuses on the parallel lives of supporting characters, as in: Tony Soprano’s daughter Meadow rebels against her family by dating an African-American Jewish student at Columbia!
Each of your acts should contain a 60/30/10 breakdown of your A, B and C-plots, respectively. In a half hour show with no C-plot, the ratio should be closer to 60/40. These are rough estimates, however, and you should feel free to take liberties in how you organize your story. The bottom line is to keep your show moving.