Brief description.

Arc x - And a title for the arc, if you want one

Player Characters

Write in a little list of PCs, you know, just for giggles.

Major NPCs

A list of major NPCs.

Common Opponents

A list of common opponents. Not sure if this is a good category or not. Your call.

Major Locations

A list of major locations. Write it down, because your players? They've already forgotten.