Firstly, I need to provide my definition of some words if you haven't read role playing games before:
NPC
Non Playing Character - Something that has intelligence that can interact with players.
Creature
Any object, animal, evil/neutral/good NPC, etc. that can attack players
The Dungeon
This is a good example of how things can be dynamic. Most adventures will have a creature in each room of a castle, underground cave, luxurious mansion, etc. But I always feel that once the players start fighting loudly with the first creature, all the other creatures will join the fight! So I often will have something that I think should be a bunch of small fights, into one large one. I'm not sure if this is right or wrong with may adventures I prepare for, but its how I run games. And the players normally enjoy it much more since it is more realistic of how those creatures would react to the combat situations.
The Story
This is often pre-defined by an adventure path, book, scenario, etc., but I think this should be very dynamic as well based upon the players and/or parties motivations for playing in the first place.