This is just on the fly without my checklist in front of me:
Grounding
Build to test bench
Hardware Diag - CPU, HD, RAM, Mobo, GPU, PSU Voltages
Build/Assembly to Chassis
BIOS Settings
OC tweaking
Hardware Diag - CPU, HD, RAM, Mobo, GPU, PSU Voltages, USB Ports etc, All IO
Wire Management
OS Install/Activation
Drivers/Patching/Software/AV
Benchmarking
Temp Testing - CPU, GPU, Ambient
Positive/Negative pressure airflow tests (Fans)
Final Hardware Diag - All