Draw the space you have to work with for the atrium using graph paper for an informal approach or architectural drawings for a highly technical approach. If you are designing lighting and decor for an existing atrium, draw the space as is. If you are designing the atrium itself, draw the physical space within which you must situate the atrium. You may wish to make photocopies of the drawing so you can experiment with multiple design possibilities.
Make a list of the various requirements the atrium must fulfill, including user needs, functions, such as like hosting events or having space for a visiting artist, safety requirements and basic physical considerations like ventilation and lighting. Being threshold spaces -- that is, spaces through which a person passes between the outside world and the interior of a building or home -- atria should have durable flooring that will stand up to tracked-in mud and snow.
Sketch design possibilities for the atrium, keeping in mind both the functional and aesthetic considerations for an entry space. Experiment with different pedestrian "flow" possibilities. Add the decorative touches that typically come at the end of the design process. For example, featuring plants in the atrium provides a pleasant view from near or far, adds a touch of nature, and even helps filter the air. Benches, tables, fountains and sculptures are other common furnishings and decorative items in atria.
Check your favorite design against the list of requirements and relevant government building codes to make sure you have included every critical feature and met every requirement. Adjust the design as necessary. Some specific, special requirements for atria include smoke management and skylights maintenance, according to the Whole Building Design Guide.