The Klingon death ritual was a Klingon rite performed during, or directly following, the death of a warrior.
The Ritual involved opening and staring into the eyes of the dying individual, then bellowing loudly at the sky. The latter served as a warning to the dead (presumably in Sto-vo-kor): "Beware, a Klingon warrior is about to arrive".
Once the Ritual was completed, the body was unceremoniously discarded in whatever manner was most convenient. It was considered to be "only an empty shell" which should be treated as such. (TNG: "Heart of Glory")
It was extremely rare for non-Klingons to witness the Klingon death ritual. (TNG: "Heart of Glory")
The first such case was believed to be in 2257, when L'Rell was called upon to perform the ritual. After Lieutenant Ash Tyler was discovered to be the Klingon sleeper agentVoq, and in danger from having two sets of memories in his system, L'Rell attempted to heal him by exorcising the remaining memories of Voq. Afterward, L'Rell, realizing that Voq was truly gone, performed the death ritual for her old friend. (DIS: "Vaulting Ambition")
In 2364, Korris, Konmel, and Worf performed the rite, following the death of Kunivas. Soon after, Worf performed the Ritual for Korris, after being forced to kill him when Korris threatened the ship. (TNG: "Heart of Glory")
Worf was last seen performing the ritual in 2375, after slaying Gowron in personal combat. In this instance, Worf opened the slain warrior's eyes. (DS9: "Tacking Into the Wind")
The fact that the opening of the eyes was not done for K'Ehleyr and Jadzia would seem to suggest that this aspect of the ritual is unnecessary or inappropriate for a fallen mate or for females, or that Worf was too distraught to open their eyes.
Evidently, not all Klingons observe this ritual. None of the Klingons aboard Kronos One performed the ritual for Gorkon in Star Trek VI: The Undiscovered Country (though doing so would have created a possible contradiction by having Kirk and McCoy witness it); none of Duras' comrades appeared to perform the ritual for Duras in "Reunion" (nor did Worf, though he may not have considered Duras worthy of such a ritual); and Kor did not perform the ritual for either Koloth or Kang in "Blood Oath".
Ak'voh, the act of watching over a fallen warrior's body, was an ancient Klingon tradition. (DS9: "The Ship")
This tradition seems to be inconsistent with the belief that after death, the body is only an empty shell; however, since Worf calls the ak'voh an ancient tradition, perhaps it reflects an earlier conception of the journey to Sto-vo-kor, that, while likely no longer commonly practiced, Worf was familiar with due to his studies of ancient Klingon culture. It is also to be noted that Worf performed this for crewmanEnrique Muniz, a Human, and perhaps since the ak'voh is much like an Irishwake , he may have felt this would have been a more appropriate and respectful gesture to join Miles O'Brien in doing so.
R'uustai, or "The Bonding", is a rite of brotherhood sometimes performed after the death of an individual's parents. (TNG: "The Bonding")
If an individual dies in a manner that does not ensure entry into Sto-vo-kor, his or her relatives may fight a great battle in the deceased's name; a victory will allow him or her to enter Sto-vo-kor. (DS9: "Image in the Sand", "Shadows and Symbols")