According to tradition, one can begin to greet others with L'Shana Tova (Have a good year) from Tu B'Av (the 15th day of Av). In as much as I am writing this on Tu B'Av I want to bless everyone already with a year of good health, spiritual growth, deep Torah learning, the highest Shabbeses, livelihood, peace in the home, peace in our hearts and peace in the world.
And now comes the question - why do we begin this greeting from Tu B'Av which is 45 days before Rosh Hashana and not Rosh Chodesh Elul which may seem a more likely time as Elul comes exactly one month before Rosh Hashana and the whole month of Elul is considered preparation for a new year.
According to Chassidut and Kabbalah the fact that Tu B'Av is 45 days before Rosh Hashana is very significant and is connected to the Talmudic debate over which month the world was created in: Tishrei, the month in which Rosh Hashanah, the New Year of years falls, or Nisan, the month in which Pesach falls and which is the New Year of the months (Rosh Hashanah 11a). Both sides make numerous arguments, but the Talmud reaches no definitive conclusion. Rabbeinu Tam, a later commentator, explained the underlying unity of both opinions: the world was created in potential or in thought in Tishrei and in actuality in Nisan.
The word for "thought" in Hebrew is machshava. When those letters are permuted the spell choshav-mah, "to think of mah [the essence of a matter]" Mah = 45; thus one can read this allegorically as: God began to think of creating the world 45 days before Rosh Hashana!!
What this tells us is that we too should already begin the process of thinking about the essence of our lives and how we can be better, stronger, deeper.