An important rule while creating a vignette is to group different elements of different sizes. They should not stand with same size competing with each other. Essentially one requires a mix of vertical object, horizontal object and something that bridges both. For example if you have a vase or a table lamp(a vertical object), you can add books as horizontal element and say a small sculpture bridging between the high and the lows in the arrangement. Just like the below:
The little Buddha is bridging between the books and the lamp. It is an important element here else our arrangement will look incomplete.