"The Nasi":

Cf. Siddur, p. 368-371

[Every day from Rosh Chodesh Nissan until the twelfth of the month, usually after Shacharis,] one reads the passage [from Bamidbar 7-8:4] that describes the offering brought on that day by a particular Nasi, or tribal prince, for the dedication of the altar of the Mishkan.

[In common parlance, each day's passage itself is often referred to as "the Nasi."]

This daily reading is followed by the prayer which opens with the words Yehi Ratzon (and which appears in Siddur Torah Or [as well as in Siddur Tehillat HaShem, p. 371]). This prayer is recited even by a Kohen or a Levi [despite its seeming relevance only to tribes other than the Tribe of Levi]. [1]

Beis Nissan:

The second of Nissan is the yahrzeit of [the fifth of the Rebbeim of Chabad,] Rabbi Shalom DovBer -- the Rebbe Rashab [5621- (1860) -5680 (1920)].

"The Rebbe Rashab passed away at about 4:30 a.m. on Motzaei Shabbos Parshas Vayikra, before daybreak on the second of Nissan, 5680, in Rostov [on the River Don], and his resting place is there." [2]

"At about twenty minutes after four, with the approach of dawn on the second day of the first month, the highest heavens opened up, and the pure soul ascended -- to pour itself forth into its Father's bosom. With a holy sweetness, with a noble tranquillity, our holy master handed over his soul to G-d, the L-rd of all spirits." [3]

Yud-Alef Nissan:

The eleventh of Nissan is the birthday of the seventh of the Rebbeim of Chabad, Rabbi Menachem Mendel Schneerson -- the Lubavitcher Rebbe Shlita, who was born in 5662 (1902), and assumed the mantle of leadership in 5710 (1950). [4] May he be blessed with long and happy years!

Yud-Gimmel Nissan:

The thirteenth of Nissan is the yahrzeit of the third of the Rebbeim of Chabad, Rabbi Menachem Mendel -- the Tzemach Tzedek, who [was born in 5549 (1789) and] assumed the leadership in 5588 (1827). [5]

"Moreover, we must inform you of the passing of our holy master during the night preceding Thursday, the thirteenth of Nissan, 37 minutes after ...[6] a.m. " [7]

This was in 5626 (1866); his resting place is in the village of Lubavitch.

Shabbos HaGadol: [8]

The Haftorah beginning Ve'arva (Malachi 3:4-24) is read only when Shabbos HaGadol falls on erev Pesach. This passage tells of the tithe that was to be brought to the storehouse [of the Beis HaMikdash], and the time for clearing one's home of tithes (in the fourth and seventh years of the Sabbatical cycle) was erev Pesach.

Following the ruling of the Shulchan Aruch, end of sec. 430, after Minchah on Shabbos HaGadol we read part of the Haggadah, from Avadim Hayinu until Lechaper al kol avonoseinu, because the redemption and the miracles began on the Shabbos before Pesach. [9]

The Sale of Chametz:

It is not the custom in the Rebbe's household to make the rav an agent for the sale (mechiras chametz); rather, the leaven is sold to him outright, with an areiv kablan, a third-party guarantor. [10]

The Search for Chametz:

The search for leaven (bedikas chametz) takes place after Maariv. [11]

It is customary in the Rebbe's household to place ten pieces of hard bread in various places, each wrapped in paper.

One searches by the light of a beeswax candle (Shulchan Aruch, sec. 433) and with a feather.

The chametz found is placed in a small paper bag. After the search one places the bag, together with the feather and any remnant of the candle, in a wooden spoon. All this is then wrapped in paper (except for the spoon handle which remains uncovered), and bound several times with string, which is then knotted.

Erev Pesach:

From the morning of erev Pesach until after the korech of the Second Seder it is our custom not to eat any of the ingredients of the charoses or maror.

"Some time after writing the above," [notes the Rebbe Shlita,] "I read that certain people are accustomed not to eat chazeres [for a certain time] before Pesach, and that this was the custom of the Rashba."

Shemurah Matzah: [12]

The Rebbe Shlita has asked everyone, especially rabbanim, shochatim and anyone else involved in communal activities, to endeavor to distribute round, hand-baked matzos -- specifically shemurah -- to their acquaintances, sufficient for at least both Sedarim

People organizing communal Sedarim, in hotels and the like, should also attend to this. [13]

The Rebbe Rashab used to be present at the baking of shemurah matzah after midday on erev Pesach. He would join in the Hallel, interrupting his recitation -- even in the middle of a chapter -- to direct the kneading, baking, and so on. [14]

It is the custom of the Rebbe Shlita to distribute shemurah matzah after Minchah on erev Pesach, at which time he wears the silk surtuk (frock coat) of Shabbos and Yom-Tov, and a gartl. [15]

Friday Evening:

When Shabbos coincides with a Yom-Tov or Chol HaMoed, the last stanza of Lechah Dodi reads Gam B'Simcha U'Vetzhala.

When a Yom-Tov or Chol HaMoed coincides with Shabbos, the following passages are said in a whisper: Shalom Aleichem, Eishes Chayil, Da hi Seudasa, Mizmor L'Dovid. [169]

Festive Joy:

Though the Torah [17] ordains that one should rejoice on Yom-Tov, one should certainly not become intoxicated, and the like; as Rambam writes with regard to simchas Yom-Tov, "One should not over-indulge in wine [18] and so on." [19]

Pesach Etiquette:

Rabbi Chayim Avraham (son of the Alter Rebbe) once visited his brother, the Mitteler Rebbe (Rabbi DovBer of Lubavitch), to wish him a good Yom-Tov. On that occasion he related that the Alter Rebbe had once said: "On Pesach one does not offer a visitor food and drink, but the visitor may help himself." [20]

Kerias Shema:

On the second night of Pesach, the Prayer Before Retiring at Night follows the same order as on any other festival. [21]

Footnotes: 

1. HaYom Yom, p. 41.
(According to the instructions given for this reading in Siddur Torah Or and Tehillat HaShem, on the thirteenth of Nissan one should read [the summarizing paragraph which begins] Zos Chanukas Hamizbe'ach (i.e., from Bamidbar 7:84 to 8:4).

This would appear to be an oversight, because in his Shulchan Aruch (429:15) the Alter Rebbe writes that on the thirteenth day one should read from [the beginning of] Parshas Behaalos'cha until kain asah es haMenorah (i.e., Bamidbar 8:1-4), a passage that corresponds to the Tribe of Levi.

The above comment is among the last of the notes with which R. Avraham Chayim Naeh introduces his Piskei HaSiddur.) The actual practice to be followed requires clarification. 

2. From Chanoch LaNaar (Kehot, NY), p. 16; see also HaYom Yom, entry for 2 Nissan. Regarding the circumstances of his passing, see Ashkavta DeRebbe [by Rabbi Moshe DovBer Rivkin; Vaad LeHadpasas HaKuntreis, NY, 1953]. 

3. From a letter of the Rebbe Rayatz, published in Chachmei Yisrael Baal Shem Tov [and in Igrois Koidesh (Letters of the Rebbe Rayatz), Vol. I, p. 110]. 

4. For an outline of the biography and activities of the Rebbe Shlita, see the introductory summary in HaYom Yom (bi-lingual edition, pp. A19-A26). [See also Yemei Melech (a documented biographical study of the Rebbe Shlita), compiled by Rabbi M.M. Laufer (Kehot, Kfar Chabad, 1989; 3 vols., Heb.).] 

5. For his biography, see the Appendices to the Responsa entitled Tzemach Tzedek, in the section dealing with Orach Chayim; see also [the Biographical Appendix to] Derech Mitzvosecha, collated by the Rebbe Shlita; and see Beis Rebbe, Part III. 

6. The manuscript page is torn at this point. 

7. From the manuscript book known as "87-Schneiderman," p. 49a. 

8. The majority of the following customs of the Pesach season are taken from the Haggadah shel Pesach im Likkutei Minhagim VeTaamim [compiled and edited by the Rebbe Shlita. Page references in the present work are to its bi-lingual edition (see footnote 226 above), here referred to in brief as Haggadah for Pesach.] See there at length. 

9. See Haggadah for Pesach, p. Aleph. 

10. HaYom Yom, p. 45. 

11. Appendix to Haggadah shel Pesach, p. 63; HaYom Yom, p. 45. 

12. [More grammatically, matzah shemurah ("guarded matzah"); i.e., matzah baked from wheat that has been guarded with especial care against dampness and consequent leavening.
"Shemurah matzah" is the inverted form of the term commonly used by Yiddish - and English-speakers.] 

13. From a talk of the Rebbe Shlita on Shabbos Mevarchim Nissan, 5714, which appears in full [in Yiddish] as an appendix to the second edition of Likkutei Dibburim, Likkut 23; for English translation, see Likkutei Dibburim, Vol. V. 

14. HaYom Yom, p. 45. 

15. Such was the practice of the Previous Rebbe in his latter years. 

16. HaYom Yom, p. 46. 

17. This obligation applies likewise today; see: Rambam, Hilchos Yom-Tov 6:17-18; Chinuch, Mitzvah 488; Shulchan Aruch (Beis Yosef and Alter Rebbe), Orach Chayim, end of sec. 529; and elsewhere, including Shaagas Aryeh, where this view is expounded at length in sec. 56. It differs from Tosafos, s.v. Asah, in Moed Katan 14b. See also Sdei Chemed, Divrei Chachamim, sec. 84

18. Hilchos Yom-Tov 6:20-21. See also Shulchan Aruch, end of sec. 529, which quotes the above words of Rambam, and adds (presumably in order to conclude on a positive note), "...but all should be holy," in the spirit of the teaching in the Yerushalmi (Yevamos 2:4) and in Vayikra Rabbah (24:6), that "one who keeps his distance from promiscuity is called kadosh, holy" - and it is this that the Shulchan Aruch alludes to in its reference to transgression. (Note of the Rebbe Shlita.). 

19. From the Introduction by the Rebbe Shlita to Kuntreis No. 100. 

20. HaYom Yom, p. 47. [The reason: to avert embarrassing a visitor who may have undertaken certain stringencies involving his Pesach food.] 

21. See the section referring to "Prayer before retiring at night. page 49 in the printed version.