The Rebbe's guidance on the practical side of mourning — Kaddish, the year of mourning, yahrzeit customs and the tombstone:
Kaddish and the year of mourning. On mourning practices according to Chabad custom, including Kaddish, see IK 412, 917. A mourner customarily says the Kaddishes of the prayer service — the sources for about sixteen Kaddishes a day are explained in IK 4946 — and on how long Kaddish is said, see IK 851. When no mourner is present, the customary Kaddishes of the prayer service are still said (IK 3260). Kaddish D'Rabbanan is said after learning Mishnayos (IK 3410, 5149). An avel should not lead Hallel before the amud (IK 4008), and follows local custom when leading prayers (IK 9154, 3382). When burial is delayed, see IK 536; for a child who passed away young, see IK 7074. Arranging Kaddish and Mishnayos is valuable, but living deeds matter even more (IK 7880); involvement in pure Jewish education may even take precedence over saying every Kaddish (IK 7292, 7272). A wedding may be set during the year of mourning, following tradition (IK 8255).
The yahrzeit. A yahrzeit brings elevation to the departed soul and to those left behind (IK 1543). When a yahrzeit falls on Shabbos, observe the weekday customs beforehand, and don't fast on Shabbos (IK 5094, 2367). When the date of passing is unknown, or the passing was in another place or time zone, follow the guidance of a Rav (IK 2816, 4667, 537). On yahrzeit customs, see also IK 424, 455, 512, 518, 3098.
The tombstone. Don't delay erecting a matzeivah unnecessarily; honoring a parent's grave with a tombstone is urgent (IK 7605, 6032, 8269). Follow local custom in placement and wording, consult the local Rav on the inscription, and be careful with truthfulness in what is written (IK 2967, 7544, 8934, 8362).
See also: Mourning and loss – Grief, comfort and honoring the departed; Faith and Chassidus – Hiskashrus (the yahrzeit of a tzaddik).