1) Many have the custom to fast on the eve of Rosh Hashanah. Nevertheless, after the afternoon services they eat something, so that they do not enter the festival while fasting. (Kitzur Shulchan Aruch 128)
2) On the eve of Rosh Hashanah a person should occupy himself with Torah and good deeds, and repent especially for those sins which are between a man and his friend. He should make sure to ask forgiveness from his friends early, and not wait until the eve of Yom Kippur. (ibid)
