React has become the default for building modern web applications, which means most teams inherit a React codebase rather than start one. The patterns that keep those codebases healthy are less about clever abstractions and more about discipline at the boundaries.
Start with data flow. Colocate state as close to where it is used as possible, and be deliberate about what gets lifted. Most performance complaints we are asked to diagnose trace back to a single piece of state living several levels too high in the tree.
Second, treat the server/client boundary as an architectural decision. In the App Router, a component is a Server Component until you say otherwise. Pushing 'use client' to the leaves rather than the root routinely cuts a bundle in half.
Third, memoise deliberately, not defensively. useMemo and React.memo have real costs and only pay for themselves when the work they guard is genuinely expensive or the props are genuinely stable.
