From the onset of Adar one should magnify his joy. If a Jew has a dispute with a non-Jew he should take him to court during Adar since it is an auspicious time for Jews. (Taanit 30a)
The Steipler, Rabbi Yaakov Yisrael Kanievski, would drink a little wine on Rosh Chodesh and on Rosh Chodesh Adar a little more than he was used to drinking. One does not necessarily have to drink wine, but can find other ways to make it a joyous day.
The Ohev Yisrael, zt”l, the Rabbi of Apt, writes that the word “b’simcha” has the same numerical value as the word “shana,” year. The more b’simcha, joyous, one is during Adar, the more joy one will experience the entire year!
The Chidushei HaRim, zt”l, states that just as we go into the illumination of Tishrei through Elul, we attain the dveikut, or intimate connection with Hashem, of Nisan through Adar. In Adar, our repentance is born of love and is stronger than the teshuva of Elul which is rooted in fear.
Rav Shneur Zalman of Liadi, the first Rabbi of Chabad, said that Yom Kippurim is really Ke'Purim (like Purim). This means that on Purim we have an opportunity to regain our closeness to G-d even if we have not fulfilled his will properly, even more than on Yom Kippur. This is related to the idea of the Chidushei Harim, that via love we can achieve more than through fear of G-d.
Let us rejoice in our service of G-d and attain through this joy a special relationship wish Hashem.