Pictures are the best way to describe these elements.
Scale is defined as how big or small objects appear in a room. This element is hard to execute, but when done properly, looks amazing. The object above this bed is rather small in comparisons to the rest of the room and the space on the wall, but it piques your interests and adds an asymmetrical feel to the bedroom. The picture below depicts scale on a larger verison with the huge purple lamp in the corner!
Shape is an easy element because most objects have a distinct shape about them, but it is especially intriguing when the shapes are odd, very small, or really big, and mixed with other different shapes.