To place the flag at half-staff (or half-mast, on ships), hoist it to the peak for an instant and lower it to a position half way between the top and bottom of the staff.
The flag is to be raised again to the peak for a moment before it is lowered.
On Memorial Day, the flag is displayed at half-staff from sunrise until noon and at full staff from noon to sunset.
The flag is to be flown at half-staff in mourning for the death of designated, principal government leaders. The flag is to be flown at half-staff for thirty days in mourning for the death of the current or former President of the United States.
The U.S. flag is otherwise flown at half-staff (or half-mast on ships) only when directed by the President of the United States, or (only for buildings within his or her jurisdiction,) the Mayor of Washington, D.C.
When used to cover a casket or coffin, the flag should be placed with the union at the head and over the left shoulder.
It should not be lowered into the grave; it is also to be removed before the casket is set for cremation.
It is considered a proper sign of courtesy to salute a casket covered with the American flag as the pall (in military and state funerals) at the proper time.
The U.S. flag is to be flown at half staff on Peace Officers Memorial Day, May 15. 4 U.S.C. §7(m) except when May 15 is also Armed Forces Day which falls on the third Saturday of May, upon which the flag should be flown at full staff.
The U.S. flag is to be flown half staff on Patriot Day (September 11)
It is probably not proper U.S. flag etiquette to lower the flag for a death at a place of business for example.
Thanks for the post. In particular, I didn't know about the Memorial Day rule.