Hilchos Sefirah
382. If one missed one day of counting Sefiras Ha'omer (or counted incorrectly ie. counted the wrong day) one should continue to count each subsequent day, but without a beracha.
Shulchan Aruch w/Mishnah Brurah 489:8
 
383. However, one should, if possible, hear the beracha said by someone else (and answer Amein) to be able to fulfill the mitzvah properly, with a beracha.
Shulchan Aruch w/Mishnah Brurah 489:8
 
384. If one forgot to count at night one should count anytime during the following day without the beracha. One may then continue to count on subsequent nights with a beracha.
Shulchan Aruch w/Mishnah Brurah 489:1
 
385. If one is uncertain as to whether he missed the previous day's counting he may continue to count with a beracha. Shulchan Aruch w/Mishnah Brurah 489:8 see also Bi'ur Halacha
 
386. Women are not obligated in the mitzvah of counting the Omer because it is a positive mitzvah that is dependent upon time. However, many women have accepted upon themselves to count, while others have the minhag for women to refrain from counting.
Shulchan Aruch w/Mishnah Brurah 489:1, Minchas Chinuch 306, Avnei Nezer 384
 
387. Women may, if they wish, count with a beracha, but their husbands should remind them to count so that they do not miss any days. The minhag of the Steipler was for women within his household to count with a beracha. Orchos Rabbeinu 2:pg92, Piskei Tshuvos 489:7
 
388. One may count the Omer in any language, however one must understand what he is saying. Shulchan Aruch w/Mishnah Brurah 489:1
 
389. One should L'chatchila count while standing. However, bi'dieved, if one counted while sitting he is Yoitze. Shulchan Aruch w/Mishnah Brurah 489:1
 
390. One must count the correct day of the Omer as well as the number of weeks. If one neglected to count the weeks he should count again without a beracha. If he neglected to count again, he may nevertheless continue to count subsequent days with a beracha.
Shulchan Aruch w/Mishnah Brurah 489:1
 
391. However, if one only counted weeks and neglected to count the days one is not Yoitze and it is as if he did not count at all. Shulchan Aruch w/Mishnah Brurah 489:1
 
392. During the days of Sefirah we do not make weddings, listen to music, or cut hair, because at this time the 24,000 talmidim of Rebbi Akiva died so we keep some minhagim of Aveilus. Shulchan Aruch w/Mishnah Brurah 493:1
 
393. However, according to the psak of R' Moshe Feinstein, one may make a wedding before Rosh Chodesh Iyar, or after Lag Ba'omer, and invite guests who may be keeping sefirah at that time, and they may participate in the dancing with music.
Igros Moshe OC 1:159, 2:95, EH 1:97
  
394. Engagements are permitted throughout the days of Sefirah with a Seudah. Music and dancing however is not permitted between Rosh Chodesh Iyar and Lag Ba'omer.
Shulchan Aruch w/Mishnah Brurah 493:1
 
395. Before Rosh Chodesh Iyar and from Lag Ba'omer on, one may be lenient and rely upon the opinions of the Poskim who permit music at a Seudas Mitzvah.
Shulchan Aruch w/Mishnah Brurah 493:1, Piskei Tshuvos 493:5
  
396. There are two minhagim of Aveilus during Sefirah. One minhag keeps Aveilus from after Pesach until Lag Ba'omer, and one minhag keeps Aveilus from Rosh Chodesh Iyar until Lag Ba'omer and from the day after Lag Ba'omer until Shavuos, (ie. three days before Shavuos).
Shulchan Aruch w/Mishnah Brurah 493:3
 
397. If one is part of a Kehilla (Congregation) where everyone follows one minhag, (ie. Chassidim who follow the minhag of the Rebbe) one must keep that minhag. Otherwise it is permitted for one to choose either minhag and change from year to year. Shulchan Aruch w/Mishnah Brurah 493:3, SV Chasam Sofer 142, SV Minchas Yitzchok 4:84
  
398. If a Bris Milah occurs during Sefirah it is permitted for the Sandik, Mohel and father of the baby to take a haircut on the day before the Bris (in the late afternoon) in honor of the Bris. {If the Bris is on Shabbos they may take a haircut even Friday morning.}
Shulchan Aruch w/Mishnah Brurah 493:2
 
399. It is permitted to cut hair on Lag Ba'omer regardless of which minhag Aveilus one is keeping, unless one is following the minhag of the Arizal which does not permit cutting hair even on Lag Ba'omer and even for a Bris.
Shulchan Aruch w/Mishnah Brurah 493:2, Shaarei Tshuvah 8
 
400. One should not move into a new home or apartment during Sefirah because it causes extra Simcha (and according to some opinions it requires a beracha of Shehechiyanu.
Shulchan Aruch w/Mishnah Brurah 493:1, Piskei Tshuvos 493:1
 
401. If one is forced to move during Sefirah it is best to move on Rosh Chodesh or on Lag Ba'omer. {Some opinions are lenient and permit moving into a new home during Sefirah}.
S"U Avnei Tzedek YD 44
 
402. According to the Mishnah Brurah one may make a Shehechiyanu during sefirah (eg. on eating a new fruit or upon wearing new clothing. Those who follow this opinion buy new clothing during sefirah. Shulchan Aruch w/Mishnah Brurah 493:1, Piskei Tshuvos 493:2,3
 
403. However, other poskim disagree, and therefore many have the minhag to avoid eating new fruits or wearing new clothing during sefirah. {Some permit it on Shabbos, and Lag Ba'omer}. Some who follow this opinion do not buy new clothing during sefirah. Piskei Tshuvos 493:2,3
 
404. The minhag of not listening to music during sefirah includes live music, recorded music, and according to some opinions, even singing songs in a group setting (except for Shabbos zemiros which is permitted, and at a Seudas Mitzva which is a machlokes). Igros Moshe OC 1:166, 3:87, YD 2:137, SV Minchas Yitzchok 1:111, SV Yechave Da'as 3:30, SV Oz Nidbiru 10:23, 8:58, SV Shibolei Haleket 8:127, SV Tzitz Eliezer 15:33:2
 
405. According to the psak of R' Shloma Zalman Auerbach one may sing songs in a group setting which are "Dveikus" type songs, which will not lead to dancing. An individual may sing any type of song because generally it will not lead to dancing.
Bein Pesach L'Shvuos 15:5, Orchos Rabbeinu 2:pg95
  
406. The minhag not to take a haircut during Sefirah is equally applicable to men and women. However, in an instance of necessity or mitzvah (eg. a girl preparing for her wedding, a woman going to the mikvah, or a married woman with hair that is difficult to keep under her shaitel) it is permitted for a girl or woman to cut her hair.
Igros Moshe YD 2:137, SV Lehoros Nosson 2:32, see also SA 551:MB79
 
407. It is permitted for a woman to pluck her eyebrows, and it is permitted for a man to cut the hair on his mustache if it is causing difficulty eating. Bein Pesach L'Shvuos 9:11 citing R'Shloma Zalman Auerbach, see also SA 551:12,13, Piskei Tshuvos 493:7
 
408. There are several reasons for the Simcha of Lag Ba'omer.
1) On Lag Ba'omer the talmidim of Rebbi Akiva stopped dying. (Mishna Brurah 493:MB8),
2) This is the Yahrtzeit of Rebbi Shimon Bar Yochai and on this day he revealed the Zohar. (Sdei Chemed, Chida, Bnei Yissaschar, Chayei Odom, Aruch Hashulchan, Kaf Hachaim).
 
409. 3) On Lag Ba'omer Rebbi Akiva gave Semicha to his five talmidim who did not die, and through whom Torah was disseminated, (among them Rebbi Shimon Bar Yochai).
(Sdei Chemed, Chida, Kaf Hachaim, Pri Chodosh),
4) On this day The Mann began to fall for Klal Yisroel in the Midbar

(S"U Chasam Sofer YD 233).
 
410. This coming Monday is Pesach Sheni, and it is also the second Monday in the series of fast days following Pesach knows as Be'hab. According to many opinions one does not fast on this day, make Hespedim, or a Hakomas Matzeivah. Rather the fast day is pushed to either the following Thursday or Monday. Piskei Tshuvos 492:1
 
411. There are different minhagim regarding the saying of Tachnun, El Erech Apayim, or Lamenatzeach on Pesach Sheni (as it is not mentioned in Shulchan Aruch to omit these tefillos). Many have the minhag to eat Matzah on Pesach Sheni by day, zecher L'korbon Pesach. Piskei Tshuvos 492:1
 
412. One does not say Tachnun on Lag Ba'omer (or by Mincha on erev Lag Ba'omer). Some (most minhag Sefard) also do not say Lamenatzeach or have aveilim daven for the amud.
Shulchan Aruch w/Mishnah Brurah 493:2, Piskei Tshuvos 429:5, 493:2
 
413. According to the Ra'mah one should not take a haircut (or shave) on Lag Ba'omer at night; rather, one should wait until morning. However, many Achronim are lenient and do permit taking a haircut at night. Shulchan Aruch w/Mishnah Brurah 493:2
 
414. Some do not fast on Lag Ba'omer even for the yahrtzeit of a parent, while others have the minhag to fast. There are also different minhagim with regard to a Chosson and Kallah fasting when they are getting married on Lag Ba'omer.
Shulchan Aruch w/Mishnah Brurah 568:MB37, 573:MB7
 
415. One of  the earliest sources for the minhag to go to Meron (the place of the grave of R' Shimon bar Yochai) on Lag Ba'omer and light a fire in the zchus of R' Shimon bar Yochai is from R' Chaim Vittal in the name of the Ari Hakodosh and Rabbeinu Ovadiah M'Bartenurah.
Sefer Gal Peninim
 
416. Many have the minhag to bring their sons who are three years old to have the first haircut at Meron and thereby perform the mitzvah of leaving the Peios of the head uncut. This minhag is mentioned by R' Chaim Vittal as "an age old minhag" at the time of the Arizal.
Sefer Gal Peninim
 
417. The reason for the minhag for children to play with a bow and arrow on Lag Ba'omer is because chazal say (Yerushalmi Berachos 9:1) that during the life of Rebbi Shimon bar Yochai there was no rainbow ever seen. A rainbow and a bow are both called a "keshes". Many great Rebbes practiced this minhag. { B'gematria - Hakeshes  = Rabban Shimon ben Yochai}.
Sefer Gal Peninim citing R' Menachem M'Riminov and The Bnei Yissaschar
 
418. Many have the minhag to throw valuable clothing dipped in olive oil into the fire lit in the zchus of Rebbi Shimon bar Yochai, and it said that the Or Hachaim Hakodosh practiced this minhag. Some poskim however (eg. The Ba'al Shoel Umashiv) decried the minhag as being Bal Tashchis, while others defend it. Sefer Gal Peninim