Loosen the main blade grip bolts so the main blades move freely.
Hold the helicopter so the right side or left side is facing down.
Turn the main rotor hub so the blades are parallel to the ground.
Tighten the blade grip bolts just enough so the blades won't droop much when the heli is lightly shaken. If You overtighten the main blade grip bolts, then the main rotor blades will not straighten out at full headspeed and this will cause vibration.
If you are having too many boom strikes later, you can tighten the blade grip bolts after running up the heli to full headspeed to ensure the blades have straightened out.