With the rapid growth of IP networks in South-Asia in the past few years, and the advent of new services and applications -- be they wireless/wireline broadband Internet access, cable telephony, VoIP, remote teleconferencing, e-governance, or mobile entertainment -- a key issue before carriers is how to design and operate their networks as methodically and as efficiently as possible to maximize both customer retention and profits. While several best practices typically emerge from each provider\'s unique situation and cumulative experience (the "art" of network design), there are certain operational precepts that systematize and streamline the complex, multi-dimensional task of designing and managing modern, operational IP networks (the "science" of network design). In this talk, we first discuss the overall network design process and the manner in which control over the network must be exercised at varying timescales to achieve efficient operation. Next we discuss the functions that the operational, engineering, and planning teams at a carrier must typically execute, their inter-relationships, and the importance/rationale for performing them to optimize network performance. We then outline some network design best practices that have evolved over the past decade, drawing upon examples of carriers such as Sprint, Global Crossing, AT&T, NTT, and Reliance. We conclude with a look at some automated traffic engineering and planning tools, and how they enable carriers to rapidly identify potential performance problems, rigorously experiment with/evaluate design options, perform thorough scenario and network analysis, and develop robust designs.