The Laws of Rosh Hashanah, part 1 vol. 3, no. 24
Selichos According to the Ashkenazic custom selichos are recited starting the Sunday before Rosh Hashanah (this year coinciding with Septemebr 8). Since the selichos service is generally recited very early in the morning, one should be careful that he does not recite the blessing on the talis before the proper time.
Annulling vows There is a long standing custom to perform the service of annulling one’s vows the morning before Rosh Hashanah (this year coinciding with September 13). The service can be found in most siddurim. Shabbos This year the first day of Rosh Hashanah falls out on Shabbos. This causes many significant changes in the order of the day. The most obvious change is that we do not sound the Shofar on Shabbos. We omit the prayer Avinu Malkeinu. The Tashlich service is postponed until the second day. Kabalas Shabbos is performed by reciting only the two psalms Mizmor Shir L’yom Hashabbos and Hashem Malach. The additions for the Shabbos davening are recited.
Additions to Prayers From Rosh Hashanah until Yom Kippur we add special phrases to our Shemone Esreh. In the first blessing we add zachreinu l’chaim; in the second blessing we add mi chamocha; in Modim we add uchsov l’chaim; and in Sim Shalom we add b’sefer chaim. If one forgot to say any of these additions he does not have to repeat the blessing.
However, if one forgot to say the different ending of the third blessing, Hamelech Hakadosh, he must return to the beginning of the Shemone Esreh. If one forgot to say the main addition of the Rosh Hashanah Shemone Esre, Uvchen pachdcha, but concluded the blessing properly with hamelech hakadosh he does not need to repeat the blessing.
