The Rebbe's guidance on the chassidic holidays — Yud-Tes Kislev, Yud Shevat, Yud-Beis–Yud-Gimmel Tammuz and Chai Elul — and how to mark them:
Yud-Tes Kislev. Yud-Tes Kislev, the day of the Alter Rebbe's liberation, is the "Rosh Hashanah of Chassidus," an annual renewal of learning and living Chassidus (IK 1263, 4199, 6019). It reveals the essential inner point of every Jew (IK 3202), and its vitality should carry through the whole year (IK 4027, 4977, 5028, 5935, 6048). Mark it with farbrengens full of life and joy (IK 1261, 7929, 8076), learn Chabad Chassidus from its foundational texts (IK 7503), and reach out to include those who don't yet know Chassidus (IK 4981, 5874). The customary wish is "Kesivah vachasimah tovah" in learning and the ways of Chassidus (IK 3250, 7191). The days from Yud Kislev to Yud-Tes Kislev are a preparation (IK 8260), and Yud-Tes Kislev and Chanukah share a mission (IK 3099, 8919).
Yud Shevat. On Yud Shevat, the Previous Rebbe's yahrzeit, gather to learn the maamar "Basi LeGani" (IK 884, 8002), increase in Torah study, especially Chassidus, and in prayer and kindness (IK 3348, 8587, 9642). Hold lively farbrengens with joy and song (IK 8759, 9451, 10321). On that day his merit brings blessing to all who follow his ways (IK 1412, 5116b), and the day should inspire renewed dedication to his mission (IK 9816, 9824). On how to observe it — prayer, study, tzedakah and more — see IK 885.
Yud-Beis–Yud-Gimmel Tammuz. The days of the Previous Rebbe's liberation are days of redemption for every Jew, and powerful times to draw blessing (IK 637, 5573, 7703). Prepare for them with renewed energy in outreach and personal growth (IK 5529, 6928), celebrate with joyful farbrengens (IK 7361, 9931), draw strength from his self-sacrifice to stand firm (IK 5603, 5607, 8858), and let their inspiration follow the Previous Rebbe's own wishes and last all year (IK 3632, 6956).
Chai Elul. Chai Elul brings vitality to every part of the Elul service (IK 1191, 1210, 3777) and is marked by farbrengens (IK 128, 8220, 7435).
For all of them. Prepare communal events thoroughly and involve many people (IK 5543, 6283), turn resolutions into action (IK 1324, 5083), and report on what was done (IK 1325).
See also: Teshuvah – Elul, Rosh Hashanah and the Ten Days; Jewish outreach – Spreading Chassidus; Torah study – Learning Chassidus.