The Shabbat preceding Pesach is called Shabbat Hagadol (the Great Shabbat), because of the great miracle that occured that day.
On Shabbat Hagadol, after minchah, we recite the Haggadah from “We were slaves” to “to atone for all our sins”; for that day marks the beginning of the redemption and its miracles.
It is customary to put pieces of hard bread in various places some time before the search, so that the one who searches will find them.
According to the Kabbalah, one should place 10 pieces.
Before starting the search, the following blessing is recited:
Blessed are You, L-rd, our G-d, King of the universe, who has sanctified us with His commandments and commanded us concerning the removal of chametz.
One is to search by candlelight in all hidden places, even cracks in the floor.
One is not to speak between the blessing and the beginning of the search, even concerning the search itself.
Throughout the search one should not speak about anything that is not relevant to the search.
Members of the household should stand nearby to hear the blessing, with each one then searching his own place without speaking in between.
Take heed to search first in the room nearest the place where the blessing was heard, and not to go to another room immediately after the blessing.
After the search one must be careful that the chametz retained to be eaten or to be burnt in the morning, be put in a safe place, so that it not be carried about and thereby crumbled and spread by children or rodents.
After the search one must also nullify [the chametz he may have overlooked] and say:
All leaven and anything leavened that is in my possession, which I have neither seen nor removed, and about which I am unaware, shall be considered nullified and ownerless as the dust of the earth.
On the fourteenth of Nissan; in the fifth hour of the day, one should make a special fire and burn the chametz and nullify it.