The Rebbe's guidance on the days from Pesach to Shavuos — Sefiras HaOmer, Pesach Sheni, Lag BaOmer and Shavuos:
Sefiras HaOmer. The counting is a time of steady refinement of one's character, each day building on the one before, never standing still (IK 6229, 4278, 7655); it prepares us to receive the Torah (IK 2616, 6855). Chabad's custom is to study Tractate Sotah during Sefirah (IK 2687, 6897). Avoid crossing the International Date Line during Sefirah if possible (IK 7543, 9464; see IK 6298, 494). On stringencies in counting, see IK 9759. An upsherin should generally not be held during Sefirah but on Lag BaOmer (IK 2091, 2624, 2671, 2539), and a wedding is best set after Shavuos rather than on Lag BaOmer (IK 2571).
Pesach Sheni. Pesach Sheni teaches that nothing is ever lost — it is never too late to make up what was missed (IK 8816, 8817, 7747). It also teaches that one must actively spread Chassidus, not only guard it (IK 7305). On the customs of eating matzah on Pesach Sheni, see IK 371.
Lag BaOmer. On Lag BaOmer Rashbi opened a channel for all Jews to the inner dimension of Torah; it is a time to learn and spread Chassidus with joy and love for fellow Jews (IK 601, 603, 1002, 7639, 8820, 7301). Prepare Lag BaOmer activities and involve all the students (IK 4328, 4270), and keep up good traditions such as student trips to Meron (IK 3439). Children's blessings on Lag BaOmer have special power (IK 10771). Its joy should extend through the year (IK 10772).
Shavuos. Receive the Torah with joy and with inner depth (IK 4422, 8428, 8634, 6886). Before Shavuos, take responsibility for the Torah education of children — ours and others' (IK 1029, 3531, 8429), and give tzedakah (IK 9500). Its inspiration should last all year (IK 7663), and the tashlumin days after Shavuos allow one to complete what was missed (IK 7667). On the all-night vigil and praying afterwards, see IK 2861; on reciting Sefer Yetzirah on Shavuos night, see IK 8227.
See also: Shabbos and holidays – Pesach; Parenting – Naming a baby and the upsherin; Jewish outreach – Spreading Chassidus.