How do I maintain consistency across changes?

As an e-commerce business owner, I'm struggling to maintain consistent performance and strategy across multiple marketing channels, product updates, and team changes. Every time we implement a new initiative or hire new team members, our conversion rates and brand messaging seem to fluctuate. I need a systematic approach to ensure that our core strategies, brand voice, and operational standards remain stable and predictable, even during periods of growth and transformation. What are the most effective methods for creating and maintaining organizational consistency?