1) From the beginning of the month of Elul until after Yom Kipur, when writing a letter to a friend a person must mention at the beginning or end that he wishes to bless him that he will merit to be written and sealed in the book of good life during the days of judgment which are coming for good. (Kitzur Shulchan Aruch 128)
2) Men of good deeds have the custom to check their Tefillin and Mezuzos during this month, and to correct any faults they have in fulfilling other commandments. (ibid)
