Orient the diorama box vertically or use an unusual container. People often use a shoebox tipped on its side horizontally to hold their diorama. Start with a more creative base to open it up to new ideas. For example, a vertical box lends itself to lots of hanging elements at different heights. Another idea is to use multiple boxes or containers to display different scenes or levels from the same biome. An aquarium lets you design a diorama that can be viewed from all sides.
The purpose of a diorama is to extend the scene you are creating beyond two dimensions, as in a photograph or drawing. If you simply draw a background and place some figures on the bottom of the diorama, you aren't taking full advantage of the medium. Remember to use all the sides of the container; extend paper foliage or creatures from the sides and hang birds and clouds from the top. Working in three dimensions creates depth, so don't forget to stagger the elements of your scene from front to back inside the container to get the best use of the space.
One of the great things about making a diorama is that is brings a scene to life. Simply placing the correct landscape, plants and animals together in a box demonstrates a basic knowledge of a particular biome, but putting the elements together in a way that shows the relationships between them demonstrates a more complex understanding of how biomes work. Telling a story also makes your diorama more interesting to viewers and offers them something to think about. Your story could show anything from predators versus prey to a weather event.
Take your diorama to another level by adding other forms of media. Sound and light make your project more interesting and can enhance the storytelling aspect of the project. Use a heat lamp to intensify a desert biome diorama, or play ocean sounds to evoke a beach atmosphere for a diorama displaying a coastal biome. An approach that utilizes more of the viewers' senses is engaging and memorable.