The major contributions of our work include adopting the NFR framework to represent and analyze two software qualities that often conflict with each other: maintainability and performance. We identified and described many heuristics that can be implemented in a system's source code to achieve either quality. We implemented some of the heuristics in two medium-sized software systems and then collected measurements to determine the effect of the heuristics on maintainability and performance. A general methodology is described for evaluating and selecting the heuristics that will improve a system’s software quality the most.