The Shulhan Aruch (Orah Haim 262:3) rules that before Shabbat begins one must put on his finest clothing in honor of Shabbat. The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933; listen to audio recording for precise citation) notes that this Halacha applies even if one spends Shabbat alone in his home and will not be going out, or if he is traveling or spending Shabbat with only non-Jews. The requirement of wearing fine clothing on Shabbat is intended as a display of honor to the Shabbat, and not to give honor to other people. Therefore, wherever one spends Shabbat, he is required to wear his fine clothing.
The Mishna Berura then cites a comment from the Sefer Hasidim (Rabbi Yehuda HaHasid of Regensburg, Germany, 1140-1217) that one should not hold a baby on Shabbat before placing a cloth on himself to protect his clothing from becoming soiled. Given the importance of wearing fine clothing on Shabbat, one must take precautions to ensure that his clothing will remain clean and will not become dirtied.
The Shulhan Aruch writes that one should accept Shabbat with joy, and go out to greet it just as one would greet a king, or a bride and groom. Commenting on this Halacha, the Mishna Berura records the custom of turning to the western wall of the synagogue when reciting "Bo’i Kalla," in order to greet the Shabbat. There is a controversy among the Halachic authorities as to whether one must turn specifically to the west, or if one should turn to the entrance, wherever it is located. The work Hut Shani (Rav Nissim Karelitz, contemporary) maintains that one should turn toward the door to greet the Shabbat, as though greeting a distinguished guest. Wherever the entrance to the sanctuary is located, that is where one should face when greeting the Shabbat. According to this view, the Mishna Berura mentions the west only because synagogues back then were built with the entrance on the west wall, and therefore the congregation should turn to face wherever the doorway is. Others, however, disagree. The Kaf Ha’haim (Rav Yaakob Haim Sofer, Baghdad-Israel, 1870-1939), in Siman 262 (Se’if Katan 32), cites the Arizal (Rav Yishak Luria of Safed, 1534-1572) as saying that one should face specifically the west, as this is the direction where the sun sets. This is the ruling of Rav Moshe Feinstein (Russia-New York, 1895—1986), in his Iggerot Moshe (Orah Haim, vol. 3, 45), and this is the Halacha. Therefore, regardless of where the entrance to the sanctuary is situated, the congregation should face toward the west while reciting "Bo’i Kalla."
I was recently in a synagogue in Los Angeles in which the Hechal (ark) is, strangely enough, situated to the west. (Apparently, it was originally built by a non-Orthodox congregation that did not follow the Halacha requiring that the ark be positioned to the east.) For the recitation of the Amida, the congregation must turn around and face east, as it is forbidden to recite the Amida with one’s back turned to the east. But for greeting the Shabbat when reciting "Bo’i Kalla," the Halacha is that they should remain facing west, in accordance with the Arizal’s position, as discussed.
Summary: One must wear his finest clothing on Shabbat, even if he is spending Shabbat alone or with only non-Jews. One should also ensure that his clothes do not get dirty on Shabbat. The congregation turns to the west to greet the Shabbat when reciting "Bo’i Kalla" in the Kabbalat Shabbat prayer service. They turn to the west regardless of where the door to the sanctuary is situated.
