1) Every person must search his deeds and repent of the bad ones during the ten days of repentance. One needs more repentance for an act about which he is unsure if it was bad than for an act which was definitely bad, for one who knows that he has sinned will regret it more than someone who is unsure. (Shulchan Aruch 603)
2) The entire nation of Klal Yisrael have the custom to increase their good deeds and donations to charity and to occupy themselves with good deeds and the commandments between the new year and Yom Kippur more than on all the other days of the year. All also have the custom to arise during the night during these ten days to pray in the synagogues with supplications and beseechings until the light of day. (Rambam in the laws of repentance)
