Seliḥot are recited with a minyan, because the Thirteen Attributes of Mercy are “devarim she-bikedusha” (holy words), which may only be recited in a quorum of ten (SA 565:5). Of course, a minyan is also required for the recitation of the half Kaddish at the beginning of Seliḥot and the full Kaddish at the end. If the time to recite Seliḥot arrives and there is no minyan yet, the congregation should recite Ashrei, the supplications, and the piyutim while skipping the Thirteen Attributes and the paragraph that introduces them. When the tenth man arrives, the congregation should first recite three verses, follow them with the half Kaddish, and then say the Thirteen Attributes from then on, in their assigned places (MB 581:4).
One who is in a place without a minyan for Seliḥot may recite them on his own. However, he must either skip the Thirteen Attributes or read them with the cantillations, as if he were reading from the Torah. Some say he should also skip the Aramaic prayers (SA 565:5; MB 581:4), while others disagree (Kaf Ha-ḥayim 581:26; see Harḥavot).
Even though there is no mitzva to wear a talit at night, according to Ashkenazic custom the ḥazan for Seliḥot wears a talit to honor the prayers and the congregation (MA 18:2; SHT 581:3). Yemenite custom is for all male participants to wear a talit. According to Sephardic practice, the ḥazan for Seliḥot does not wear a talit. After all, he does not wear it for Minḥa, and certainly not for Ma’ariv and Seliḥot, which are recited at night. However, if the ḥazan is not dressed respectably, for example if he is not wearing a jacket, it is proper for him to put on a talit (R. Eliyahu, cited in Mikra’ei Kodesh: Rosh Ha-shana, p. 72, n. 35).
If the service is at night, the ḥazan does not recite a berakha when putting on the talit, as there is uncertainty. According to Rosh, one recites a berakha when putting on a talit at night, whereas according to Rambam, one does not, and in cases of uncertainty about berakhot, we are lenient and do not recite them (Levush 581:1; see MB ad loc. 6). Some ḥazanim make a point of borrowing a friend’s talit (having in mind not to acquire it); since a borrowed talit does not require tzitzit, everyone agrees that a berakha is not recited over it (Taz 581:2).
Even in the presence of a bridegroom or the father (and other honorees) of a child on the day of his brit mila, the vidui and Taḥanun of Seliḥot are nevertheless recited. Some disagree with this; nevertheless, it is the common practice. Since reciting Seliḥot is not absolutely obligatory, it is preferable for a newlywed or someone making a brit not to attend. This way, the congregation does not face uncertainty.
Sephardim say some of the Seliḥot sitting and others standing. Yemenites recite most of them while sitting, while Ashkenazim stand for all of them. Those who find it difficult to stand may sit. They should try to stand when reciting vidui and the Thirteen Attributes, as well as when the ark is open. The elderly, the weak, and the sick who find even that too difficult may sit for the entire service. (See section 12 below.)