Halachos for Purim 1
1) Chazal have instituted that on Purim one should drink more than his usual share of wine. According to some opinions it is a Mitzvah to actually get intoxicated on Purim.
Others maintain that actual intoxication is not mandatory, rather one should drink until he gets tired, and falls asleep. This is based on the words of the Talmud (Megilah 7b) “Chayav Inish L’Besumei B’Puraya Ad D’Lo Yada Bein Arur Haman L’Baruch Mordechai- one is obligated to drink on Purim until he cannot distinguish between “cursed is Haman” and “Blessed is Mordechai”.
There is a plethora of ways to understand the above Gemara, according to Halacha and Hashkafa as well as Kaballah, and covering all of them is beyond the scope of this forum. (For those who are interested in delving deeper into this, please start with the following sources: Shulchan Aruch, Ram”a and Mishna Berura Siman 695, Aruch HaShulchan Siman 695:2-5, Yad Ephraim to Shulchan Aruch ibid., MaHarsha Megilah 7b)2) If by getting drunk, one will come to be lax in Mitzvah observance, or will Chas V’Shalom transgress sins (as is unfortunately the case sometimes, as intoxication in a non Torah environment often leads to promiscuity) , he is forbidden from getting drunk. (Meiri Maseches Megilah 7b (quoted in the Biur Halacha), Ran ibid., Shl”a ibid., Bais Yosef Siman 695 and Chayei Adam)
The point of drinking on Purim is to help us reach a higher level of Ahavas Hashem, loving our father in heaven. If one drinks in a manner that will bring disgrace to Hashem’s name, not only has he not fulfilled the Mitzvah, he will also bear a very grave sin.
Halachos for Purim 2
1) Although Purim is a Yom Tov on which work is permitted, the prevalent custom is not to work on Purim [day]. One who works on Purim will never see any blessing from the money he/she earns that day. (Some are lenient on Purim eve, in cases of great necessity) (Shulchan Aruch and Ram”a Siman 696:1. See also shu”t Chasam Sofer Siman 195)
Some people are stringent and also refrain from work on Shushan Purim. Others say this is only stringency for women. (Shl”a). Shushan Purim is also a day of Simcha, and one should try and make a small Seudah with meat and wine. (Ram”a 695:2)
2) Although it is customary to dress up in costumes on Purim, care must be taken that men do not don women’s clothing, and vice versa as doing so is a biblical transgression of “Lo Tilbash” as well as being a problem of Pritzus. This applies to children as well, and G-d fearing people should not treat this lightly. (Mishna Berura Siman 696:30 and Be’er Heitev Os 13. See also Aruch HaShulchan and Siddur Ya’avetz who are very stringent with this.)
Care should also be taken to ensure that the costumes do not contain Sha’atnez (materials of wool and linen together) as that is also a biblical transgression, and may not be transgressed even on Purim. (ibid.)