"Scenes are what allow writers to abide by the timeless saying 'show, don't tell," (Justine Schofield)
What constitutes a scene? Justine Schofield says that three things call for a scene change when a new character is introduced, a current character exits or the setting changes.
Author of The Plot Whisperer Workbook, Martha Alderson (http://janefriedman.com/2012/08/29/7-elements-scene) recommends that you generate a scene list. What does the main character want? What steps will she take to get it? What is stopping her at every turn? Is the protagonist moving the scene forward? Title each scene, or chapter if its a book, to keep track of them.
Ms. Alderson maintains that scenes have different layers, each which has a function. The first layer establishes the setting of the story. Justine Schofield mentions an exercise: write down ten items in a room. See how you can use those items to advance the scene. For example, the main character might be so worried, he eats a whole loaf of bread. He might push his desk chair out from under him because he is so frustrated. He might, in a rage, throw a cup of coffee at his sibling.
The second layer of the scene allows the dramatic action to unfold. This scene should be filled with conflict, tension and suspense. The conflict doesn't have to be overt, but it should be there. Setbacks and failure experienced by the protagonist lead to suspense. Will or will he not succeed? A change in emotional development in the main character is the third layer of the scene. The main character should have a emotional reaction to the dramatic action in each scene. A fourth layer should ensure that the details in the scene support the dominant theme of the story.
So what are you waiting for? Get out your building blocks and start building.