Tasting the foods on Erev Shabbos:
One is to taste the Shabbos foods on Erev Shabbos [to see if they need anything added to them in order to ensure their tastiness]. [Nevertheless this was not seen to be the custom of the Previous Rebbe.] It is proper to taste each and every dish of food.
Food designated for Shabbos:
If one was given food for Shabbos it should not be eaten during the week. This is an act of piety, although from the letter of the law there is no prohibition in the matter.
Sharpening knives on Erev Shabbos:
One is to beware to sharpen the [kitchen] knives every Erev Shabbos, as preparing oneself for eating is included within the honor of Shabbos. In addition [at times] one needs to sharpen the knives for the sake of Shalom Bayis [marital harmony], such as if the blade has dulled and one is unable to cut with it.
One should be careful to sharpen the knives on Erev Shabbos. This is done for honor of Shabbos and for purposes of shalom bayis.
 Kaf Hachaim 250/5 in name of Mateh Moshe 308
 Shaareiy Halacha Uminhag 1/130
 This can be learned from the law in Rama 494/2 that a pauper may decide to do whichever he wants with the charity money that he receives, even though the donors gave it with a specific intent. [So is implied from Admur’s reference to this chapter].
 This is further hinted to in the words “And prepare Es/that which you brought” and a knife is alluded in the word “Es”, from the wording of “Lesim Ulemizmoros”. Thus implying in the verse that one is to prepare the knives before Shabbos. [ibid]
 This is learned from the verse “And you shall know that your tent is in harmony” and the Sages expounded this to be referring to the sharpening of a dull knife for the sake of Shalom Bayis. [Ibid]