How do I keep code clean and maintainable?

Core principles

• SOLID — single responsibility, open/closed, Liskov substitution, interface segregation, dependency inversion
• DRY, KISS, YAGNI — don't repeat knowledge, keep it simple, build only what is needed
• High cohesion, low coupling — modules do one job and depend on abstractions, not internals
• Clear naming and small functions — code is read far more often than written
• Composition over inheritance; prefer immutability and pure functions where practical

Design patterns (Factory, Strategy, Observer, Adapter, Repository, CQRS…) are named solutions to recurring problems — apply them when the problem appears, not in advance.

Technical debt. Track it explicitly, refactor continuously under test coverage, and schedule paydown; do not let it accumulate silently.

Tooling: formatters, linters, static analysis and type systems enforce the baseline automatically.