Before the night of the 14th of Nissan everyone is required to clean his home and his place of work, including the machsan and any other storage areas in his home (such as above the bathtub, underneath the sinks), as well as the outdoor areas at home and at work. It is necessary to clean both one’s personal car and one’s company/work car. Any place or item of furniture which is used in the home or at work must be cleaned so that there is no chance chametz is left there by the start of Pesach. One must also check clothes pockets, especially in children’s clothing, as well as all kinds of bags (especially school bags) to ensure no chametz is left in them.
A person is required to be meticulous about cleaning the whole house so that not even the smallest amount of chametz remains in his possession on Pesach. The students of the Arizal said that someone who is careful not to have even a tiny piece of chametz in his possession on Pesach is guaranteed to avoid sin the entire year. (See Shulchan Aruch, Orach Chaim 447:1)
Places which tend to contain crumbs need to be cleaned very well, such as between the rubber lining on the fridge/freezer doors, the corners of the oven door, and the corners of the bread bin. (The bread bin should be kept outside the kitchen during Pesach.)
One has to be very scrupulous in cleaning the kitchen since chametz is there all year round, and so one must clean the fridge and all the cupboards very well. Since one does not actually put hot chametz in the cupboards or the fridge the only concern is that perhaps crumbs of chametz will remain. Therefore, to make them useable for Pesach one merely needs to clean them well. Those places which are very hard to reach, such as the groove behind the rubber lining on the fridge door, should be cleaned with plenty of detergent or other cleaning product which will ensure that any chametz remaining there will be unfit for consumption even by a dog. There is no obligation to take off the rubber in order to get underneath it to remove the crumbs – it is sufficient to make any crumbs stuck there unfit for consumption by a dog.
In the past, when the shelves in the kitchen were made from solid wood, there were often cracks in them which might contain chametz and it was hard to clean them thoroughly. Therefore, the Acharonim ruled that one should cover the shelves with paper or cloth, and the Mishnah Berurah (451:115) writes that the minhag is indeed to cover the shelves. (This is based on the fact that if even one crumb of chametz fell into a dish of food on Pesach it would prohibit consumption of the whole dish, since chametz on Pesach is not batel (nullified) even when it falls into a mixture a thousand times its volume.
Since pouring boiling water on tables (in order to kasher them) would presumably damage modern-day tables it is necessary to clean them very thoroughly and then cover them with a thick plastic tablecloth for the duration of Pesach. This creates a permanent chatzitzah (separation) between the table and the food and utensils used on Pesach. One should spread the tablecloth over the plastic cover. It is a good practice to avoid placing hot pots and pans directly on the table – instead one should place them on an inverted plate or something similar.
It is praiseworthy not to keep real chametz in the house with the plan to sell it to a non-Jew, unless destroying the chametz would result in a hefsed merubah (substantial loss) – such as if someone owned a shop which sold chametz. The wise man plans ahead, ensuring to use up or give away whatever chametz is left in the house from Rosh Chodesh Nissan onwards so that it will all be gone by Erev Pesach. Obviously one should not buy more chametz products in that time period. Despite the fact that we try to get rid of all chametz before Pesach, the custom is for everyone to sell their chametz to a non-Jew for maybe they missed something in their searching.
If someone leaves home after Purim and will be away until after Pesach, it is recommended he leave one room that will not been sold to a non-Jew in order to fulfill the mitzvah of bedikas chametz (searching for chametz). This should be done the night before his departure. Alternatively, he can appoint a shaliach (a representative) to search his house on the night of 14th of Nissan with a brachah, in which case he does not need to search it the night before he himself leaves.