Preparing the Haftorah:

One is to prepare the Haftorah prior to reading it.[1] Accordingly, the custom is to read the weekly Haftorah to oneself each week as part of Shnayim Mikra on Erev Shabbos in order so one be familiar with the Haftorah in case he is called up for Maftir, as explained next. It is proper to also review it again prior to going up for Maftir, and so was the custom of the Rebbe Rashab.[2] This should certainly be done if one did not review it by Shnayim Mikra.

Reading the Haftorah on Erev Shabbos:[3] Although from the letter of the law there is no obligation to read the weekly Haftorah to oneself each week, nevertheless the custom is to do so.[4] [On a Shabbos that there are two Haftoras for that week, such as the Shabbos of the 4 Parshiyos, Shabbos Rosh Chodesh, Shabbos Machar Chodesh, Shabbos Chanukah, then one is to read both the Haftorah of the weekly Parsha and the Haftorah which will be read in Shul.[5] Accordingly, if Rosh Chodesh is two days and falls on Shabbos and Sunday, one is to read three Haftora’s; the weekly Parsha, the Haftorah of Hashamayim Kisi and the Haftorah of Machar Chodesh.[6] On Shabbos Chol Hamoed Sukkos and Pesach one is to read to himself both the Haftorah of the Parsha of the coming week and the Haftorah which is read that Shabbos.[7]]

[1] See Admur 285:10; M”A 285:12; Terumas Hadeshen 101; Kneses Hagedola 285; Moreh Baetzba 4:132; Ben Ish Chaiy Lech Lecha 11; Kaf Hachaim 285:36; Sefer Haminhagim p. 49 [English]; Hayom Yom 30th Sivan

[2] See Toras Menachem 15:134 that the Rebbe Rashab was once called up to Maftir and first went into a side room to prepare the Haftora; Leket Halichos Uminhagei Shabbos Kodesh p. 38

[3] Admur 285:10

[4] In order so one be familiar with the Haftorah in case he is called up for Maftir. [Admur ibid] This custom is likewise recorded in Sefer Haminhagim p. 49 [English]; Hayom Yom 30^th Sivan.

Nevertheless from the fact that it is our custom to read all the Haftoras of a coming week, even the one which will not be read in Shul such as when Rosh Chodesh falls on Shabbos, makes it evident that this reason alone cannot be the full reason behind reading the Haftorah. This would likewise apply even in accordance to the ruling of Admur in the Shulchan Aruch [see next footnote] that only the Haftorah which will be read in Shul is to be read, as in conclusion Admur rules that when Sos Asis will be read as Haftorah many consecutive weeks one is to read to himself on the second and onward Shabbosim, the weekly Haftorah rather than Sos Asis.

Custom to read also the Haftorah with Targum: Some have the custom to read the Haftorah Echad Mikra Vetargum. [M”A 285:11] Others are not accustomed to do so. [Mateh Yehuda 285:8; Kaf Hachaim 285:38] This is not the Chabad custom.

[5] Sefer Haminhagim p. 49 [English]; Hayom Yom 30^th Sivan

The ruling of Admur in the Shulchan Aruch and other opinions: In the Shulchan Aruch 285:10 Admur rules that in a week that there are two applicable Haftoras, one is to read only the Haftorah which will be read in public and not the Haftorah of the weekly Parsha. Accordingly, on Shabbos Rosh Chodesh or Erev Rosh Chdoesh one only reads the Haftorah of Rosh Chodesh and not of the weekly Parsha. [Admur ibid; M”A 285:12] The simple reason behind this ruling is as Admur ibid explains that the entire custom to read the weekly Haftorah is only in order so one be prepared in case he is called up to read it. Hence in a week that it is not being read there is no custom to review it. [Admur ibid] Some Poskim rule one is to only read the weekly Haftorah and not the additional Haftorah that is read in public. [Kneses Hagedola 285; Moreh Baetzba 4:132; Ben Ish Chaiy Lech Lecha 11; Kaf Hachaim 285:36 that so is custom.] Our custom is to review all the applicable Haftoras.

[6] Likkut Dinei Rosh Chodesh 10:12 based on Sefer Haminhagim ibid

[7] Hisvadyus 1985 Vol. 1 p. 351