What words can I use instead of efficiency?

Words you can use instead of efficiency depend on context but include many synonyms that capture different nuances of doing things well. Common alternatives include productivity which emphasizes output per input, effectiveness which focuses on achieving desired results, proficiency which emphasizes skill and competence, competency, capability, efficacy which emphasizes power to produce effects, economy which emphasizes thrifty use of resources, orderliness, organization, system, methodicalness, and streamlined which implies smooth optimized processes. In business contexts you might use performance, output, throughput, optimization, cost-effectiveness, or resourcefulness. For personal work habits you might use time management, industriousness, or diligence. In engineering contexts you might use performance ratio, yield, or coefficient of performance. For example instead of saying we need to improve efficiency you could say we need to improve productivity, streamline operations, optimize resource use, enhance performance, or increase cost-effectiveness. Choosing the right synonym depends on whether you want to emphasize speed, skill, lack of waste, or achievement of goals, but all share the core idea of achieving maximum useful result with minimum wasted effort or resources.