Moving to S/4HANA requires attention to SQL patterns, usage of CDS views, and avoiding deprecated APIs. Key steps:

• Analyze custom code with ATC and runtime checks
• Migrate DB-dependent SELECTs to CDS/AMDP where appropriate
• Refactor uses of classical COLLECT/APPEND loops into set-based operations where possible
• Validate data models and check for deprecated BAPIs

These steps help minimize post-migration issues and make the codebase S/4HANA friendly.