In cities everywhere more and more people are discovering the undoubted pleasures and advantages of apartment living. Whether your apartment is in a converted house or industrial building, or forms part of a purpose-built block, successful living on one - or even two - levels depends on understanding both the flexibility and the limitations of the space available, and on making that space, no matter how large or small, work to your best advantage. As interiors doyenne Caroline Clifton-Mogg explains, the key to success is careful planning and a focused approach to both the design and decoration.