Every person is obligated to strive based on his affordability, to have elegant clothing for Shabbos. These clothing are to be designated specifically for Shabbos (and are to be nicer than the clothing he wears during the week). [Hence one is to avoid wearing these clothing at all during the week. Furthermore, even on Shabbos itself one is to avoid doing activities that can dirty the clothing. For this reason one should not hold a child (which can cause one to become dirty) unless he places a covering over his clothes.]
A Shabbos Tallis: One who is able to afford a second Tallis should have a second Tallis specifically designated for wearing on Shabbos.
Not to wear any weekday garments: There are scrupulous men which are meticulous not to wear any weekday clothing on Shabbos. They thus have an entire wardrobe of clothing designated to be worn only on Shabbos. This includes even a belt, pants, undershirt, [under garments, Yarmulke, socks, shoes, Tzitzis, hat].
Wearing a different article of clothing : It is proper for one to wear a piece of clothing or jewelry which is different than the clothing or jewelry worn during the week. This is done in order that one constantly remembers that it is Shabbos and not come to desecrate it. [Hence the custom of Jerusalemites is to wear a Shtreimal which is a completely different type of hat then the hat worn during the week, as it serves as a reminder of Shabbos.]
When on Erev Shabbos should one put on his Shabbos clothes: It is proper that one garb himself in Shabbos clothes immediately after bathing himself for Shabbos. For this reason it is proper for one to bathe himself as close to Shabbos as possible, and then immediately put on his Shabbos cloths. [This however only applies when bathing in one’s home. If however one is bathing in a bathhouse, as is customary when going to Mikveh on Erev Shabbos, then one should visit the Mikveh with plenty of time still left in the day. If one however plans to merely [rinse and then] immerse in the Mikveh, he is to visit the Mikveh as close to Shabbos as possible.]
When after Shabbos may one remove his Shabbos clothing? It is proper to wear at least some of one’s Shabbos clothing until after Havdala on Motzaei Shabbos. [Some however have the custom to not remove their Shabbos clothes until after eating Melaveh Malka. Others only remove them prior to going to sleep. It is told of the Rebbe Rashab that he would remove his Shabbos clothes immediately after Shabbos, not wanting at all to wear them during the weekday. However of the Rebbe Rayatz it is told that his father the Rebbe Rashab told him to follow the custom of Chernobyl to not change his Shabbos clothing on Motzaei Shabbos, and so is the custom of the Rebbe.]
Should one buy shoes specifically for Shabbos?
Should one make a point of wearing Shabbos clothes if he is spending Shabbos alone, or amongst gentiles?
Yes, as the clothing are not out of respect for the observers but out of personal respect for Shabbos.
What is one to do if he does not have any Shabbos clothing to wear?
He should change to freshly laundered weekday clothing. If he does not have any laundered clothing available, then he should launder them on Thursday.
Color of Shabbos attire:
There remains a difference of customs regarding the desired color of the Shabbos attire. Many wear all white, others black and others wear colored clothing. One is to follow the custom of his community. 
Wearing a silk garment/Kapata:
The Rebbe stated that married men are to strive to wear a silk Kapata/Frockcoat on Shabbos and Yom Tov. Those which do so are praised.
If one is bathing early for Shabbos when should he put on his Shabbos clothes?
In such a case one is to switch his underclothes, pants and shirt to fresh Shabbos clothes right after bathing even though there is still plenty of time left before Shabbos. However his upper clothes [such as a jacket, hat etc] he is to only put on right before Shabbos.
When are women to dress in their Shabbos clothes? 
Women, just like men, are to dress in their Shabbos clothes immediately after they shower close to Shabbos. They are to be wearing Shabbos clothes before candle lighting.
 As one is obligated to honor Shabbos through clean clothing as was explained in chapter 242. [ibid]
 Lit. One is to switch his clothing for Shabbos to nicer clothing.
 This is learned from the words of the prophets “And you shall honor Him from doing your ways”. The Sages expounded this verse to mean that one shall honor Him by designating different clothing for Shabbos in contrast to clothing worn during the week. The reason why the Sages specifically learned that one is to honor Shabbos through nicer clothing is because one’s clothing is also referred to as one’s honor, as clothing dignify a person as seen from the fact that when one arrives to an unknown community in elegant clothing, then he receives respect from the community. [ibid]
Why the above law was placed in parentheses: As for the reason that Admur places the ruling of “nicer clothing” in parentheses- See Aruch Hashulchan 262/3 which explains that only on Yom Kippur is there an obligation to wear nicer clothing than that of the week, however on Shabbos one merely has to wear a fresh pair of even weekday style clothing.
 So is implied from Admur and so explains Minchas Shabbos 72/71, based on M”A 262/2, that one is not to wear any of these clothing during the week. See Kitzur Halachos Miluim p. 57
 Sefer Chassidim brought in Bier Heiytiv 262/4; Mishneh Berurah 262/6.
 To note that the wording of the Magen Avraham 262/2 is in opposite order “One should not wear during the week any of the clothes which he wore on Shabbos”.
 So is implied from Admur and so explains Minchas Shabbos 72/71, based on M”A 262/2, that one is not to wear any of these clothing during the week.
 Seemingly the novelty in this ruling in contrast to the ruling brought above is that not only should one’s clothing be more elegant [such as a nicer white shirt], but one of those article of clothing should be of completely different style, such as a frockcoat or Shtreimal.
 Ketzos Hashulchan 115 footnote 47
 Lit. good
 Lit. good
 Lit. near sunset.
 This is done in order so one only begins dressing himself in Shabbos clothes in close proximity to Shabbos. The advantage of doing so is that it is now apparent that it is in honor of Shabbos that one is wearing them. [ibid]
 As we suspect he may come to take his time and come to transgress Shabbos.
 Ketzos Hashulchan 73 footnote 23
 So rules Kaf Hachaim 262/28 as the extra soul does not depart until after Melaveh Malka. [300/106]
 Brought in Leket Yosher that so was the custom of his teacher the Terumas Hadeshen.
 See Kitzur Halachos Miluim p. 56
 Kaf Hachaim 262/25
 Rav Poalim 4/13
 The Kaf Hachaim [ibid] however explains that even Rav Poalim holds this way only from the letter of the law, however as an act of piety he too agrees that one should have shoes designated to be worn only on Shabbos.
 Chayeh Adam 5 brought in Ketzos Hashulchan 73 footnote 20
 Ketzos Hashulchan 73 footnote 24
 The Kaf Hachaim 262/24 and 26 brings that the color of clothing which one wears on Shabbos in this world one will as well wear in the next world. He then goes on to suggest based on this that one is to only wear white clothing.
 This is based on the writings of the Arizal which says that one is to wear 4 white garments. [Beir Heiytiv 262/4] The Kaf Hachaim [262/24] strongly writes that one is to only wear white clothing on Shabbos and not other colors. He brings a story from his teacher which once had the soul of a deceased Sage reveal himself to him and tell him that he was being punished in the next world for wearing black clothing on Shabbos.
Some Poskim however discourage wearing white if it appears as an act of extra haughtiness. [Peri Megadim A”A 262] The Kaf Hachaim [ibid/26] however rules that even when there is appearance of haughtiness, such as no one else wears white clothing in that community, one may nevertheless do so, as on this is dependant his wardrobe of the world to come.
 Peri Megadim A”A 262; brought in Biur Halacha
 Shaareiy Halacha Uminhag 1/240
 Shaareiy Halacha Uminhag 5/29; Hisvadyus Purim 1955
 The concept of wearing a silk Kapata on Shabbos and Yom Tov is brought in Mamarim of the Rebbe Rashab [1902 p. 231; 1911 p. 328; 1912 Vol. 2 p. 872]. There it is explained that the reason we wear silk on Shabbos is because Shabbos receives from the world of Beriya and since silk comes from an animal which corresponds to the world of Beriya it is therefore proper to wear silk on Shabbos. Now although wool also grows on an animal, nevertheless wool is considered the level of Tzomeiach Shebichaiy, however silk is Chaiy Shebichaiy. [Toras Menachem 13 p. 309]
Wearing a coat over one’s silk Kapata: It is worthy to note the Rebbe’s custom of wearing a coat in public over his silk Kapata, whenever it was worn, even in the summer. Some write this is because it is improper for gentiles to view one wearing silk. [See “Hashabbos Bekabala Ubichassidus” p. 235]
Wearing a mixed material Kapata of wool and silk: Some quote the Rebbe to have spoken against wearing a mixed material Kapata of wool and silk. Practically a source is needed to verify this claim.
 Ketzos Hashulchan 73 footnote 24
 Vetzaruch Iyun as the implication from Admur is that placing on one’s Shabbos clothes immediately after bathing is of more importance then wearing them close to Shabbos.
 M”B 262/11; Kaf Hachayim 262/31