Use only weapons that you usually don't pay attention to for the entire match.
Use only low-damage weapons throughout the match.
Enable black and white mode and disable the interface.
Turn off color (black and white mode) and play.
Switch to left-hand mouse control (if you're right-handed) and play.
Empty your magazine completely before reloading.
Close your eyes for a few seconds after each kill.
Use only weapons of a specific cost (e.g., up to $2000).
Shoot only through smoke.
Shoot only at a specific body part (e.g., legs)."