Best Practices and Pitfalls

What works well

• Start small and iterate: Smaller, well-scoped prompts and changes outperform large, one-shot attempts.
• Ground with documentation and tests: Provide Copilot with authoritative references and fast feedback.
• Keep humans in the loop: Pair AI assistance with review discipline and explicit acceptance criteria.
• Standardise prompts: Capture effective prompts in instruction and prompt files to scale consistency.
• Prefer repeatable patterns: Apply the same approach across modules to reduce cognitive load and variance.

Common mistakes (and how to avoid them)

• One-shot prompting for large transformations → Decompose into a chain of small, reviewable steps.
• Vague instructions → Be explicit about scope, constraints, and success criteria (tests, lints, budgets).
• Overstuffing context → Reference docs via instruction files instead of pasting long text into prompts.
• Ignoring variability → If a result drifts, restate constraints, reduce scope, and try again.
• Pattern drift across teams → Use shared instructions, exemplars, and early cross-team reviews.

Validating and reviewing Copilot-generated code

• Treat Copilot as a fast pair, not a final arbiter.
• Enforce pull request hygiene: small diff size, clear intent, issue links, and passing checks.
• Require compilation, unit tests, and type checks to pass before review.
• Review for behaviour, security, performance, and style—not just syntax.
• Use checklists and CODEOWNERS to ensure the right reviewers see the change.

Iterative testing and refinement

• Prefer many small cycles (prompt → change → tests → review) over long cycles.
• Maintain characterisation tests to preserve behaviour during refactors.
• Add tests alongside changes; let tests anchor intent and protect against regressions.
• Use mutation testing or contract tests on critical paths where feasible.
• Monitor coverage trends; prioritise risky gaps rather than chasing a single target number.

Review and governance checklist

• Scope and intent are clear and limited to the stated module or interface
• Coding standards and naming conventions followed
• Tests added/updated; key paths covered; CI is green
• Security and dependency policies respected; scans are clean
• Observability updated if behaviour or interfaces change
• Documentation updated (READMEs, ADRs, or architecture notes as appropriate)

Key Takeaways

• Small, well-scoped changes with strong tests and reviews deliver safer progress faster.
• Clear instructions, shared prompts, and consistent patterns reduce variance and rework.
• Human oversight is essential: treat Copilot as an accelerator, not a replacement.
• Governance, security, and documentation must evolve with the code—not as an afterthought.
• Prioritise behaviour-preserving refactors and measurable improvements over big-bang changes.