How is it to be read?
One is to read each verse twice and then immediately read the Targum on that verse prior to continuing on to the next verse. This order is followed throughout the entire reading. Nevertheless, from the letter of the law one may read the verses with Targum in whichever order one chooses. [see footnote] Hence if one does not have a Targum available he may read the entire Mikra twice and then read the Targum when it becomes available.
The last verse:  The last verse of the Parsha is to be read a total of three times, twice before saying the Targum, and a third time after the Targum. This is done in order to complete the reading of the Parsha with a Torah verse, as was done in past times when the Targum was read during the public Torah reading, after each verse. [Nevertheless, despite this ruling of Admur in his Shulchan Aruch, it is not the Chabad custom to repeat the last verse a third time.]
May it be read in segments? May one talk in middle or take a break? Some are accustomed not to talk at all, or make any type of interval, throughout the entire reading of Shnayim Mikra. Hence they read it from beginning to end without interruption. [This is a very proper custom, and is followed by those meticulous in Mitzvos. Those which follow this custom must start over again from the beginning if they talked or made an interval in between. See Q&A!] However from the letter of the law there is no requirement to read the entire Parsha Shnayim Mikra in one period, rather one may even read only the Mikra of one section today, the Mikra of another section tomorrow and so on and so forth throughout the week. Hence one who learns the daily Chumash is from the letter of the law considered to have fulfilled the reading of Mikra [up to Shevii] one time and hence must only say the Mikra once with Targum [up to Shevii, while Shevii is said twice]. If he is accustomed to read each verse twice while learning, then he has to only make up the Targum. [Nevertheless the custom as explained above is to re-read the entire Parsha Shnayim Mikra Echad Targum on Erev Shabbos.]
Reading from a Sefer Torah: One who knows by heart the tunes [which mark the end of each verse] in the Torah reading, is proper for him to read Shnayim Mikra from a Kosher Torah scroll on each and every Erev Shabbos. [This however is not the Chabad custom, or the custom of many other Gedolei Yisrael, as by doing so one is unable to read the Targum after each verse. Hence we read it from printed Chumashim which contain Targum. One who does not know the Taamim by heart is not to read from the Torah according to all.]
Is one to read the Pasuk of Shema Yisrael twice?
The verse Shema Yisrael is to be read twice as is the law by all Pesukim. However some Poskim rule one is not to read the Pasuk twice in a row, and is rather to read a few more Pesukim in between. The custom is unlike this opinion.
Is one to read the Parsha with the tune of the Torah reading [Taamim]?
Some Poskim rule one is initially required to read the verses with their tune even when doing so from a Chumash. Practically this is the custom. Nevertheless this is not critical for fulfilling one’s obligation. Hence if one does not know the tune of the verses he is to read it without the tune. Likewise if one already read it without the tune, then even if he knows the tune, he is not required to repeat the reading.
Must the verses be read in order?
Yes. One is not to read a later verse prior to reading an earlier verse. Nevertheless, after the fact if one did not read the verse in order he has nevertheless fulfilled his obligation.
Q&A on Interruptions during Shnayim Mikra
May one learn other Mefarshim while saying Shnayim Mikra if he is stringent not to make any interruptions until he completes the reading?
No. Those which are particular not to interrupt when saying Shnayim Mikra are not to learn even other Mefarshim while saying Shnayim Mikra. They are rather to read it straight from beginning to end without any interval at all.
If one used the bathroom while saying Shnayim Mikra is he to say Asher Yatzar after leaving the bathroom if he is stringent not to make any interruptions until he completes the reading?
One is to say Asher Yatzar immediately after leaving the bathroom, and is not to delay it until later on.
May one initially use the bathroom in middle of Shnayim Mikra if he is stringent not to make any interruptions until he completes the reading?
The Ramak writes that one is not to initially use the bathroom until he finishes Shnayim Mikra even if he feels the need to go. However from the Poskim it is evident that one may certainly use the bathroom, even according to this custom.
May one who is thirsty have a drink in middle of Shnayim Mikra if he is stringent not to speak until the end of Shnayim Mikra?
If one is very thirsty some Poskim write that he may drink in middle of the reading and say a blessing before and after.
According to the stringent custom brought above is one to read the Haftorah right after he completes the reading of the Parsha without interrupting in-between?
The Ramak writes that one is to read the Haftorah immediately after finishing the reading of the Parsha without making any interruptions in-between.
Sparks of Kabala
Reason why one is not to interrupt in the midst of Shnayim Mikra:
Reading Shnayim Mikra Echad Targum has the power to create an angle. One who makes an interruption in the midst of reading it enters impurity into this angle.
 285/3 following the second custom recorded by Admur there. Admur concludes “and this custom is more proper”. So is also the practical custom as recorded in Sefer Haminhagim p. 49 [English]; Hayom Yom 30th Sivan. This was the custom of the Arizal. [M”A 285/1]
The reason for why this custom is the most proper: As this follows the same order of the Torah reading of the past which was done by reading the Targum of each verse directly after reading that verse. [ibid]
Other opinions: Some [Shalah; Rashal] have the custom to read a section [of Pesucha/Setuma] twice and then immediately read the Targum of that section prior to beginning the next section. This order is followed throughout the entire Parsha. [First opinion recorded in Admur ibid]
The ruling of the Mishneh Berurah: The Mishneh Berurah [285/2] rules that one may follow whichever opinion he chooses.
 285/3. This implies that one may even read the entire Parsha twice and only then read the Targum, or read an entire Aliyah and then read its Targum etc. This is unlike any of the customs mentioned by Admur, although as he concludes from the letter of the law all methods are valid. See also the next sentence in which Admur rules that in case of need this is the course that one is to follow [reading first the entire Mikra].
Other orders of reading: One fulfills his obligation if he read the Mikra once, then the Targum and then again the Mikra. [285/7] However seemingly this is only Bedieved, as Lechatchilah one is always to first read the Mikra twice. [Ketzos Hashulchan 72 footnote 1; Kitzur Halachos 285 footnote 6]
Vetzaruch Iyun if one fulfills his obligation if he reads the Targum prior to reading the Mikra even once. [Ketzos Hashulchan ibid; From M”B 285/6 it is implied one does not fulfill his obligation, although perhaps he too meant to leave this matter unresolved. See there.]
 Then too the last verse would be repeated after its Targum was read. [Ibid]
 Shaareiy Halacha Uminhag Vol. 5/28; However see Ketzos Hashulchan 72/3 and Kitzur Halachos 285/5 that mention this ruling without remark that this is not the followed Chabad custom.
 Shlah [Torah Oar 138a] in name of Ramak, and so is recorded also in Olas Shabbos 285/2; M”A 285/11; See next footnote. To note the Rebbe in Lekutei Sichos 24 p. 342 does not unequivocally state that it is our custom to follow this opinion and rather uses the wording “those that are stringent to follow this custom”. This is in contrast to other matters of Shnayim Mikra mentioned in the above letter in which the Rebbe explicitly states the Chabad custom.
 The Beir Heiytiv [285/1] writes “It is a great prohibition to speak in middle of Shnayim Mikra”. The M”B in Shaareiy Tziyon 285/11 explains this to refer to speaking in middle of a Parsha [Pesucha/Setuma] as it is considered like one who is interrupting his Torah study for mundane matters. However between Parshiyos everyone agrees that from the letter of the law it is allowed. Admur however makes no mention of there being any prohibition involved and rather simply mentions it as a custom. The M”A 285/11 simply writes it is proper not to talk in-between.
 M”B 285/6; So rules also Kaf Hachaim 285/32
 Lekutei Sichos 24 p. 342; Kaf Hachaim 285/32
 Vetzaruch Iyun from Admur’s conclusion “and after that one reads the Mikra in order”. What is the meaning of this? Is one required to read at least one time the entire Mikra in order? In Ketzos Hashulchan 72/2 and Kitzur Halachos this conclusion is omitted. In Kuntrus Hashulchan p. 31 [of the same author of Ketzos Hashulchan] he edits that the words should read “and after that one reads the Targum in order”. His basis is that it is untrue to say that one would be required to read the entire Mikra at least one time in order, as such a law does not exist. Hence he edits that it must have said Targum.
 Based on 285/7 regarding a Melameid Tinokos.
No leniency is however to be learned from this law regarding reading from a Sefer Torah without due reason. See Shach Yoreh Deah 270/5; Nemukei Orach Chayim 669/2 towards end; Shut Marsham 175
 Meaning that he knows by which word each verse ends. [Ketzos Hashulchan 72 footnote 1, derived from Admur’s additional word “Piskeiy Taamim”] The reason for why one must know the end of each verse by heart as a condition to read from the Torah is because it is forbidden for one to stop in middle of a verse that Moshe did not stop by [494/11], and if one does not know the end of each verse certainly he will end up stopping in middle of some of the verses.
 This was the custom of the Arizal [Shaar Hakavanos] and of the Taz [Taz 285/1]. The Taz [ibid] rules that each person should read the Mikra at least one time from a Kosher Sefer Torah, as from a mere Chumash one does not properly fulfill his obligation.
 The Arizal however would have a student read him the Targum and he would then repeat it after them. [ibid]
 Hisvadyus 1988 Vol. 2 p. 167; Lekutei Sichos 24 p. 214 footnote 59; letters printed in Shaareiy Halacha Uminhag 2/189
 As he will not know by which word to end each verse. See previous footnotes
 Ketzos Hashulchan 72 footnote 10; Shaareiy Halacha Uminhag Vol. 5/28
 Mishmeres Shalom 24
 Machazikei Bracha, brought in Kaf Hachayim 285; Ketzos Hashulchan 72 footnote 1; Kitzur Halachos 285 footnote 8;
So can also be deduced from the Peri Megadim [285 A”A 9] which rules based on 285/7 that reading the Taamim is not critical to fulfilling the obligation. This implies there is reason to assume that it should be required initially.
So can also be deduced from Radbaz brought in Magen Avraham 285 regarding one who knows the Taamim by heart that he is to read from a Sefer Torah, hence implying that all are to read the Taamim [and hence if one does not know the Taamim by heart it is better to read from a Chumash with the Taamim]. [Ketzos Hashulchan ibid]
Opinion of Admur: From Admur’s wording of “Piskeiy Taamim” which is in addition to the wording of the Magen Avraham, hence implying that the Taamim themselves need not be read. Perhaps however this is merely coming to teach that it is better to read from a Sefer Torah without the Taamim than from a Chumash with the Taamim, so long as one knows where to stop. Nevertheless even Admur would agree that when reading from a Chumash it is better to do so with the Taamim. [Ketzos Hashulchan ibid]
 Ketzos Hashulchan ibid
 Peri Megadim 285 A”A 9; Ketzos Hashulchan ibid; M”B 285/17
So is implied from the lack of this requirement or enhancement of the Mitzvah being mentioned in Shulchan Aruch. So is also implied from 285/7 regarding the Melameid who fulfils his obligation of Mikra while teaching without tune. [Peri Megadim 285 A”A 9]
So is also implied from Admur 285/4 which added “Piskeiy Taamim. See previous footnotes.
 Ketzos Hashulchan 72 footnote 5; M”B 285/6
 As even by the actual Torah reading if read out of order one fulfills his obligation.
 So is implied from Poskim brought in Kaf Hachaim 285/32 which write one is not to even interrupt Shnayim Mikra for words of Torah; So is also implied from the wording of the Ramak brought in Shlah 138a. However later on in Ramak he states that one says “Shnayim Mikra Echad Targum with Unkolus or other translation”. To note however that there he was referring to the Shnayim Mikra of the Haftorah and not of the Parsha.
 Piskeiy Teshuvos 285 footnote 30
 As he may come to forget to say it later on, as well as that perhaps he may need to go to the bathroom another time prior t completing Shnayim Mikra in which case he enters into a dispute amongst Poskim in whether he may still say Asher Yatzar/ [ibid]
 Brought in Shlah 138a; There he writes “After reciting Shnayim Mikra without any interruption, not even for his needs” In general in Halacha the term “Tzrachav, needs” refers to using the bathroom.
 Seemingly this does not transgress the prohibition of Baal Tishaktzu as one is allowed to withhold his needs for the sake of a Mitzvah. [See Admur 3/11 Basra; and Siddur as explained in Ketzos Hashulchan 19 footnote 27 that one may not use the bathroom for a bowel movement in the midst of Davening beginning from Baruch Sheamar.
 Lev Chaim 3/23 brought in Kaf Hachaim 285/15 regarding the allowance to drink in the middle
 Lev Chaim 3/23 brought in Kaf Hachaim 285/15
 Brought in Shlah 138a
 Kaf Hachaim 285/32