ABAP Performance Tuning(PDF) Tips and Tricks on

• SQL Interface
• String manipulation
• Internal Tables
• Internal tables vs Field group
• Typing
• If, Case,
• Field Conversion
• Modularization
  • Subroutines
  • Function Modules
• Tools
  • Static Analysis (Extended program check)
  • Dynamic Analysis
  • Database Access
• Getting the data / Data table identification
  • F1-F9 / Technical info
  • Runtime analysis
  • Debug
  • SE38
  • Sql trace
  • Logical database
  • Function modules
• List of important tables & Function Modules

Check out the other section on system-wide performance tuning.