Since everything we do on Rosh Ha-shana is an omen for the entire year, all should be joyful and confident that God will accept their repentance; all should be loving toward their friends and judge them favorably. One should not get angry at friends, argue with them, or speak badly of them. Apart from the prohibitions entailed by such things, they are bad omens for the upcoming year. (See MB 583:5.)
Since Rosh Ha-shana is a Yom Tov, it is a mitzva to be happy and to make others happy. Therefore, during the meals, everyone should try to make everyone present feel good. This, too, is a good omen for the whole year. (See n. 4 above; Peninei Halakha: Festivals 1:11.)
One should not sleep too much on Rosh Ha-shana, as our Sages tell us that if one sleeps on Rosh Ha-shana, his mazal – the angel charged with bringing him good fortune – will sleep all year (cited in the name of the Yerushalmi). Rather, in addition to the obligatory prayers and meals, it is appropriate to study as much Torah as possible. Nevertheless, one should not get too little sleep either, as this can disturb the ability to concentrate during prayer and study. Therefore, someone who is tired after the meal should sleep, to enable him to study properly. Some Torah greats slept on Rosh Ha-shana just as they did on other festivals (Maharam of Rothenburg). In any case, as we have seen (section 4), people should make sure to dedicate half the day to God; prayer and Torah study time should amount to at least nine hours per day.
Some avoid sleeping during the day, in hopes that this will lead to their being energetic and lively for the entire year (Rema 583:2; Mateh Ephraim). However, if someone sits around and wastes time, though awake, it is considered as if he is sleeping (MB 583:9). Most Aḥaronim, following Arizal, write that the main concern is not to sleep before midday (SAH ad loc. 8, AHS ad loc. 4; MB ad loc. 9; Kitzur Shulḥan Arukh 129:20). According to this custom, one should arise at dawn, or sunrise at the latest. If one is concerned that waking up so early will make it difficult for him to focus on prayer or to study properly, he may sleep until close to prayer time, for waking up early, though virtuous, is not as important as being focused when praying and studying Torah.
After Ma’ariv, people say to each other, “Le-shana tova tikatev[i] ve-teḥatem[i]” (“May you be inscribed and sealed for a good year”; the bracketed parts are for addressing a woman). Some say that since the judgment is sealed on Yom Kippur, on Rosh Ha-shana one should simply say, “May you be inscribed for a good year” (Vilna Gaon). This greeting is said during the morning as well, but after midday it should no longer be used, as the primary time of judgment is over. It is enough to simply wish people a “shana tova” – a good year. If the person offering the greeting adds additional good wishes, one should reply in kind. One may also reply “same to you” (“ve-khen le-mar”).
Some do not say these greetings on the second day of Rosh Ha-shana, as the primary time of judgment is on the first day. However, most people continue to extend these greetings, as judgment is inscribed on the second day, too (MB 582:25). All these customs are legitimate.