The Rebbe's guidance on the season of teshuvah — Elul, Rosh Hashanah and the Ten Days of Teshuvah (IK = Igros Kodesh letter number):
"The King is in the field." In Elul G-d is especially close and approachable — like a king who goes out to the field and greets everyone warmly — so every Jew, whatever his state, can come close (IK 735, 9540, 9544, 9550, 9727, 10462, 7745, 9209, 9360, 9363, 9558, 10205, 10465, 10471, 10891). It is a month of mercy (IK 5738, 5694) and of honest stock-taking, in which our sincere efforts are counted generously Above (IK 1185, 5748). On the Thirteen Attributes of Mercy and personal service in Elul, see IK 9020. Self-examination should be guided by the light of Torah, not only by one's own judgment (IK 9967), and personal guidance from a mashpia is especially valuable now (IK 3782, 6995).
What to add in Elul. Increase Torah study, prayer and above all tzedakah, going beyond one's usual measure (IK 2220, 7429, 9970). Say Psalm 27 each day and hear the shofar (IK 9965); on its meaning, "Hashem ori veyishi," see IK 6465. Farbrengens in Elul give extra vitality to Torah, prayer, kindness and teshuvah (IK 3791, 6492), and yeshiva students have a special task of strengthening themselves in this season (IK 751). Elul is also a time to increase outreach and influence on others (IK 529, 7738, 8667, 8671). Good thoughts even before Elul are combined Above with the deeds that follow (IK 2870). The forty days before Rosh Hashanah should be used to the full (IK 6976).
Chai Elul. The 18th of Elul brings life to every part of the month's service — Torah, prayer, kindness and teshuvah — through learning Chassidus and following its ways (IK 1191, 1210, 3777, 5743, 7752, 8669).
Rosh Hashanah. Rosh Hashanah is the "head" of the year, and its resolutions guide the whole year (IK 198, 525, 752, 10572). Its essence is crowning G-d as King through heartfelt acceptance of His sovereignty (IK 8519, 8679, 9568). Each person's shofar is a teshuvah suited to his own level (IK 524), and each has his own Divine mission for the year (IK 10211). True preparation combines personal teshuvah with acts of kindness (IK 391). On simplicity in avodah and hearing the shofar, see IK 292; on Rosh Hashanah falling on Shabbos, IK 523; on the nature of judgment, IK 300; on the creation of man and time, IK 760. Customs: the order of the Yehi Ratzon on the apple (IK 504); Selichos during the Ten Days and Tashlich (IK 302); where to daven when the mikvah is problematic (IK 3793).
The Ten Days and Yom Kippur. The days between Rosh Hashanah and Yom Kippur are a journey from outward service to inner connection with G-d (IK 102, 768), a time to seek Him with special power (IK 7016). On the avodah of Erev Yom Kippur, covering severity with kindness, see IK 299. Emotions surrounding a court case can be a lesson for these days (IK 3820). Tishrei sets the tone for the whole year (IK 3848, 9976), and one should remain for it where it matters most (IK 10731).
New Year blessings. Many letters convey the Rebbe's blessings for a good and sweet year to individuals, students, communal leaders and public officials (IK 530, 765, 9745, 9750, 10215, 10481, 10483, 10485, 10558).
See also: Teshuvah – Asking and granting forgiveness between people; Prayer – Saying Tehillim; Shabbos and holidays – The Jewish calendar; Shabbos and holidays – The chassidic holidays.