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

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