Starting thirty days before Pesah, one must ensure not to handle Hametz in such a way that it might stick to something and thus be difficult to remove before Pesah. Although one is not required to begin ridding his property of Hametz thirty days before Pesah, it is proper already then to pay attention how Hametz his handled in anticipation of the need to eliminate all Hametz from his property. This is mentioned by the Bah (Rabbi Yoel Sirkis, Poland, 1561-1640) and the Magen Abraham (Rabbi Abraham Gombiner, Poland, 1635-1682), in Siman 436.
Likewise, starting from Purim one should avoid bringing books near food, as some small crumbs of Hametz might fall into the book, and this book may then be brought to the table on Pesah. One Rabbi was of the opinion that it is worthwhile to ensure to never bring a book near food at any point during the year, and that one thereby fulfills the Misva of remembering the Exodus. Whenever a person considers bringing a book to the table and refrains from doing so because this book might be brought to the table on Pesah, he remembers the holiday of Pesah and the commemoration of the Exodus, in fulfillment of a Misva. Although this is not required according to the strict Halacha, it is an admirable practice to observe.
The Meiri (Rabbi Menahem Meiri, 1249-1310), in his commentary to Masechet Aboda Zara (5), writes that it is proper to begin making preparations for Pesah already thirty days before the holiday. This includes shopping for the materials needed for Pesah and making practical arrangements.
It is customary among many to observe the Yom Kippur Katan service on Ereb Rosh Hodesh Nissan, even among those who do not observe Yom Kippur Katan on Ereb Rosh Hodesh throughout the rest of the year. According to one view in the Talmud, the world was created on Rosh Hodesh Nissan (as opposed to the first of Tishri), and thus this day is a kind of "Rosh Hashanah," warranting a process of Teshuba in preparation for this day. Therefore, many have the custom to fast either the entire day or part of the day of Ereb Rosh Hodesh Nissan. There is also a custom to visit cemeteries on this day.
Tahanunim and Nefilat Apayim are omitted from the prayer service starting on Rosh Hodesh Nissan.
It is customary during the first twelve days of Nissan to read the section of the offerings brought by the Nesi’im (twelve tribal leaders). On each day, the verses referring to the offering brought that day are read. This custom is mentioned by the Shela Ha’kadosh (Rabbi Yeshaya Horowitz, 1565-1630). Some have the practice of conducting this reading from a Sefer Torah, whereas the custom in our community is to read this section from a printed Humash or Siddur.
It is customary to begin the reading on the first day of Nissan from the section of Birkat Kohanim, which appears immediately preceding the section of the Nesi’im. On the 13th of Nissan, the custom is to read the opening verses of Parashat Beha’alotecha – until the words "Ken Asa Et Ha’menora" – which correspond to the tribe of Levi.
Before the daily reading of the Nesi’im section, one should give some money to charity – or pledge to give some money – in memory of all the souls from that day’s tribe in need of a Tikkun (rectification). This practice is mentioned in the work Kav Ha’yashar (chapter 85). Although this custom is not commonly observed, it is a worthwhile practice to follow, as one of the important benefits of this reading is bringing merit to the deceased souls of each day’s tribe.