Working with legacy code requires a careful, methodical approach. Begin by understanding its functionality and underlying architecture. Prioritize comprehensive documentation, capturing both its current state and any changes. Implement a robust testing framework, ensuring existing functionality remains intact as you modify the system. When making changes, break tasks into manageable increments, refactoring cautiously. Establish a version control system if one isn't in place. Preserve the existing behavior until you're certain about the implications of your modifications. Collaborate with those familiar with the system, and approach changes with empathy for the original developers, recognizing that context, tools, and standards evolve over time.

They main key aspects on working with legacy code are:

Understanding and documentation

• Reading the code: before making changes, take the time to understand the existing code, even if it seems convoluted or poorly written.
• Document as you go: as you decipher the code's logic, document your understanding. This might be in the form of code comments, system documentation, or even separate notes.
• Ask for context: if possible, engage with developers who have previously worked on the codebase to gather insights.