This room is primarily task-orientated so its design will be governed by practical considerations, but once these basic needs are met, go wild - if you have to work at home, you may as well be happy in your environment!
Avoid office furniture - while the keyboard area and chair may need ergonomic design, adapting the shelving inside a wardrobe creates alternative storage. Baskets or wine racks could also replace in-trays.
Comfort zone - studies often double as guest bedrooms so a futon or sofa-bed may be incorporated anyway, but consider adding seating to this area even if it is not required as a change of perspective can aid concentration.
Wall art - a memo board may be required, but with the addition of photos or art prints it's inspiring as well as functional.
Lighting - good task lighting is vital in a study.
Striking a balance between domesticity and function in a home office is the root of successful study design.