We should wish each individual Jew and all Jews as one, Ksivah Vachasimah Tovah, Leshanah Tovah Umesukah May you be inscribed and sealed for a good and sweet year!This should be done through any available method face to face, by word of mouth or in writing. Even if we have already blessed a particular individual, we should nevertheless continue to bless them time and again throughout Elul. Our additional blessings can amplify the revealed goodness that had already been designated by Hashem for each Jew and for all Jewry to an incomparably greater extent. It is customary that even children under the age of Bar and Bas Mitzvah wish this blessing to everyone including adults.This is done, despite that fact that it is generally not considered proper for a child to bless an adult.
"It is customary to bless each other with a Kesivah Vechasimah Tovah from Rosh Chodesh Elul onward. Understandably, we should constantly amplify this custom as the month of Elul progresses from one day to the next, and certainly on special days like the 18th of Elul [the birthday of the Baal Shem Tov and the Alter Rebbe] . and yet further on the Shabbos before the beginning of the Selichos
recitation (which are begun on Motze Menuchah, .the night following [Shabbos,] the Day of Rest.. We begin reciting Selichos after most of Elul . which we spent together with .the King, in the field. . has already passed. Then, on each new day of Selichos we should yet further augment our blessing each other ...
For on those auspicious days there is a manifold and even incomparably loftier power to bless; we should therefore grab the opportunity to bless each other again
and again.. " (22nd of Elul 5748 Farbrengen, p.332-333)