Q. The Gemara teaches that when the month of Adar begins we increase our Simcha and happiness. How exactly is that reflected in practice? Do we do anything special or extra to comply with this mitzva? If not, what does it mean, since we always have to serve Hashem with happiness?
A. Indeed the Talmud (Ta’anis 29a) mentions that “When Adar enters, we increase joy." There is no mention of an increase in regard to meals eaten or other traditions to mark this time of Simcha, as would be expected.
Yet, Horav Aharon Miller Shlit’a remarked that there are some differences in Halacha, like what is mentioned in Shulchan Aruch (O.H. 688: 7) for one that is leaving for a trip where he will not be able to hear the reading of the Megila, he may prior to the start of his journey already read the Megila according to some opinions from the beginning of the month of Adar.
The other Mitzvos of Purim can only be complied with in the day itself. (See Mishna Berura ibid. 20).
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a