How do you write the “fluff” of a story and further it’s plot while not making it too drawn out or too quick?

Every scene should be moving the story along. And plots can move forward in a myriad of ways: conversations, actions, thoughts. Is your fluff contributing to and/or complimenting these things? Because you’re right: we don’t just want the bare bones of the plot, even if it’s the best plot in the world. We want the meat on the bones, too, because that gives the story its flavor. 

I know when I read, I want to taste and savor the world through the characters. But I also don’t want to be bogged down by a particular scene if it is not going anywhere or leading up to anything. So, look at the tension. If there is no tension in your scene, you might have too much fluff. Tension makes a reader keep turning the pages.