Here are Appian Interface (SAIL) best practices — clean, interview-ready, and practical:

1. Keep interfaces simple and modular; break large UIs into reusable rule-based components
2. Use rule inputs (ri!) instead of referencing records or queries directly inside the interface
3. Prefer local variables (local!) to avoid repeated calculations and improve performance
4. Avoid heavy logic in the interface; move business logic to process models, expressions, or integrations
5. Use a!refreshVariable() wisely; refresh only when required (avoid refreshAlways unless necessary)
6. Limit the use of queries inside interfaces; fetch data before loading the interface when possible
7. Use record fields instead of CDT fields for record-backed UIs
8. Design for responsiveness using columns, column widths, and stackWhen
9. Use consistent spacing, labels, and alignment for better UX
10. Prefer a!forEach() over nested loops; avoid deeply nested expressions
11. Handle null and empty values safely using a!defaultValue()
12. Apply conditional show/hide instead of creating multiple interfaces
13. Use interface tests and preview with different data sets
14. Avoid large data sets in grids; use paging and record data sources
15. Follow naming conventions for rules, locals, and rule inputs
16. Secure data using record-level security, not UI-only conditions
17. Externalize static text using constants for reusability and maintainability