Evaluate your space to decide what its main purpose is. If you have a dining room that needs to double as an office and library, focus on the main purpose of the room first. It is a space for eating FIRST, and then it is an office, and lastly a library.
Divide the space according to what you will use it for the most. Make dining a priority in the dining room and then create tucked-away space to accommodate office supplies and equipment. Use closed storage solutions for your desk area (like a computer armoire with doors) when it needs to be in an unusual place, such as your dining room. This will make your office blend in with your room and not pop out like an eye sore.