In my experience, the biggest benefit comes from having good quality integration and unit tests that are easy for the agent to run on its own to verify its work against.

Have tests, provide screenshots (or enable it to navigate the UI): https://code.claude.com/docs/en/best-practices#give-claude-a...

Typically for most code it's telling claude how to run tests.

For front end code it's giving claude a way to 'see' the work for example a Playwrite MCP server seems common. https://playwright.dev/docs/getting-started-mcp