If one forgot to add Ya'aleh Veyavo (the holiday insertion) when saying Birkat HaMazon (Grace after Meals) after a night meal of Rosh Hashanah, one should repeat the Birkat HaMazon. If one forgot to say Ya'aleh Veyavo during the Birkat HaMazon after a day meal, one need not repeat the Birkat HaMazon.
Near the conclusion of the Birkat HaMazon, after Mimarom (Siddur pg. 93), we add the Harachaman for Yom Tov and the one for Rosh Hashanah.
The prayer for Yom Tov: (Hu Yanchilaynu L'yom Shekulo Tov) should be recited before the one for Rosh Hashanah: (Horachamon Hu Yechadesh Aleinu Et Hashanah Hazot Letova Velivracha) as it is more common (tadir).
We say Oseh Shalom and not Oseh HaShalom at the end of Birkat HaMazon.
It is best for one to refrain from marital relations on both nights of Rosh Hashanah. One should not refrain if it is mikvah night.
