On the day of Lag BeOmer we increase our level of celebration a little. Some of the reasons for this practice include: on Lag BaOmer the students of Rabbi Akiva stopped dying,  Lag BaOmer is the Hilulah (anniversary of the passing) of Rabbi Shimon Bar Yochai, Lag BaOmer is the day that Rabbi Akiva gave Semicha to his new students , and is the day that the Maan began to fall in the desert. 
- Tachanun is omitted on Lag BaOmer. It is also omitted at Mincha of the day before Lag BaOmer. 
- If Lag BaOmer falls out on Sunday Tzidkatcha is omitted at Mincha of Shabbat prior to Lag BaOmer.
- One shouldn’t fast on Lag BeOmer.  However, if one’s wedding is that day one may fast on Lag BaOmer. 
- Music and dancing are permitted in order to honor the Hilulah of Rabbi Shimon Bar Yochai. 
Taking a haircut
- Ashkenazim may cut their hair on the morning of Lag BaOmer.  while some are lenient to permit it from the night of Lag BaOmer. Sephardim shouldn’t cut their hair until the morning of the 34th of the Omer.
- According to Ashkenazim, if Lag BaOmer falls out on Sunday then it’s permissible to cut one’s hair on Friday for kavod Shabbat. Some say it’s preferable to do so after Chatzot (halachic midday).  If it is difficult to cut one's hair otherwise, one may cut it from Thursday night.
- A groom, as well as the fathers of the groom and bride may shave on the 32nd day of the Omer before sunset of the 33rd. Other family members and guests should not shave before sunset.
Practices of Lag BaOmer
- Some Gedolim were very opposed to burning clothing because of Baal Tashchit (prohibition of wasting), while others defend the minhag. 
- Kohanim shouldn’t go into the room where Rabbi Shimon Bar Yochai is buried in Meyron. 
Counting the Omer
- If one has not yet counted sefira on the night of Lag Baomer, he should not tell someone that tonight is Lag Baomer. If he does, he can still recite sefira with a beracha because of the combination of the factors that 1)he didn't intend to count the day and 2) it is possible that to fulfill the mitzva of counting one must count the weeks as well as the days.
- Rama 493:2. See Chatom Sofer YD 233 writes that those who celebrate Lag Baomer for a pure intention are going to be blessed but he personally wouldn't join them because we can't establish a new Yom Tov after the destruction of the Bet Hamikdash (see Pri Chadash OC 496:14 based on Rosh Hashana 18b).
- Biur Halacha 493:2, Meiri Yevamot 62b, Kitzur S”A 120:6, Shelah Pesachim 525
- Chida in Moreh Etzbah 223 (see also Chida in Marit Ayin "Likkutim" 7), Chayei Adam Moadim 131:11, Bnei Yissaschar Chodesh Iyar 3:3
- Pri Chadash 493, Kaf HaChaim 493:26
- See Sh”t Chatom Sofer YD 233 who says that they first ate up their food for 30 days since they left Egypt and then didn't have food for three days and then they complained and maan fell. See however, Gemara Shabbat 87b and Rashi Shemot 16:1 which state that maan started on the 16th of Iyar when their 30 day food supply ran out.
- Rama 493:2, Kaf HaChaim 493:28, Mishna Brurah 493:9, Natai Gavriel (Pesach vol 3, 58:3)
- Levush 493, Natai Gavriel (Pesach vol 3, 58:4)
- Natai Gavriel (Pesach vol 3, 59:5) based on Meiri Yevamot 62b
- Halichot Shlomo 11:22
- Yalkut Yosef 493:9. Natai Gavriel (Pesach vol 3, 58:11) just writes that music and dancing altogether are permitted. He cites the Pri Megadim E”A 493:1 and Kaf HaChaim 493:9. However, those sources seem to be dealing with the days in between Rosh Chodesh Sivan and Shavuot. Yet, they may be similar to Lag BeOmer in that we don't say Tachanun perhaps granted them a quasi-holiday status.
- Rama 493:2
- Mishna Brurah 493:11 quoting the Eliyah Rabba
- S”A 493:2
- Rama 493:2. See Bear Hetiev 493:6 quotes those who are strict but ends off that if the minhag is to be lenient one doesn’t need to be strict.
- Halichot Shlomo (Chapter 11 note 79)
- Kaf HaChaim 493:23
- Rav Yisrael Belsky Piskei Halacha pg. 109–110
- Natai Gavriel (Pesach vol 3, 59:13)
- Halichot Shlomo 11:23
- Chacham Benzion Abba Shaul (Or Litzion 3:16:4)