When to start saying Selichot
- The Sephardic minhag is to say Selichot from the day after Rosh Chodesh Elul. 
- There are no Selichot on Shabbat. 
- The minhag Ashekenaz is to start saying Selichot from the Sunday before Rosh HaShana unless Rosh HaShana falls out on Monday or Tuesday, in which case, Ashkenazim start from two Sundays before Rosh HaShana. 
When at night?
- Selichot shouldn’t be said before Chatzot. 
- Preferably, Selichot should be said at the end of the night before Olot HaShachar.  However, if one delayed one can say it after Olot HaShachar. 
On Erev Rosh HaShana one should make an extra effort to get up early to say Selichot before Olot HaShachar. 
Maamer Mordechai 34:6 holds that Tikkun Chatzot precedes learning Torah and Selichot.
LeDavid Hashem Ori
- The Minhag Ashkenaz is to say LeDavid Hashem Ori once in the morning and once in the evening from Rosh Chodesh Elul until and including Shemini Aseret (and in Israel until and including Hoshana Rabba). LeDavid Hashem Ori should be said after Shacharit (after Shir Shel Yom). On days when there’s Mussaf, LeDavid Hashem Ori is said before Ein Chamocha. On Rosh Chodesh, Barchei Nafsei is said before LeDavid Hashem Ori. 
- For Spehardim it’s also proper to say LeDavid Hashem Ori after Shacharit. 
- Ashkenazim say LeDavid Hashem Ori after Mariv, however, some say it after mincha. 
- Ashkenazim start blowing Shofar from Rosh Chodesh Elul after Shacharit. 
Selichot without a minyan
- Mishna Brurah 581:4 says that an individual may say the Selichot that don’t include the thirteen attributes, or aren’t written in Aramaic.
- Mishna Brurah 581:4 writes that if there’s not a minyan when the tzibbur says Ashrei, they should wait to say Kaddish when they get a minyan. Mishna Brurah in name of the Eliyah Rabba writes that once the minyan is complete, they should continue 3 pesukim and then say Kaddish.
- Mishna Brurah 581:4 writes that if there was a minyan in the beginning and then some left, they can continue and even say Kaddish after Selichot.
- The Shliach Tzibbur should wear a Talit during Selichot, however, he shouldn’t make a Bracha before Olot HaShachar and to remove himself from doubt he should borrow a Talit from a friend (and not a public Talit) and have Kavana not to acquire it but to use it for respect. 
- Any Jew is fit for being a Shliach Tzibbur as long as the congregation accepts him. 
- Preferably, the congregation should carefully choose a proper Shliach Tzibbur who is married, thirty years old, and the more he is learned and practices good deeds the better.  However, someone who is learned and Yireh Shamayim is preferred over someone who lacks these qualities but fits the requirements of being married and thirty years old. 
- If one wear Tzitzit earlier than Olot HaShachar (for example, for Selichot) and then afdter Olot HaShachar (and preferably after MeSheyakir) puts on a Talit,
One should only make one Bracha on Tzitzit and Talit even if one puts on Tzitzit a long time before the Talit. 
- A bachur who doesn’t wear a Talit should be careful to make the Bracha on Tzitzit right after Olot after feeling the Tzitzit. 
However, if someone who slept in the Tzitzit all night, Mishna Brurah 8:42 writes that one shouldn’t make a Bracha on it in the morning (and he shouldn’t remove the Tzitzit so as to make a hefsek in order to require a Bracha).
- S”A 581:1 writes that one should starting saying Selichot from Rosh Chodesh Elul. Mishna Brurah 581:1 explains that S”A means from Rosh Chodesh and not Rosh Chodesh itself. So writes the Maamer Mordechai (Rav Mordechai Eliyahu) 34:1 as the Sephardic minhag.
- Maamer Mordechai (Rav Mordechai Eliyahu) 34:2 writes that there are no Selichot on Shabbat.
- Rama 581:1 writes that the minhag Ashekenaz is to start saying Selichot from the Sunday before Rosh HaShana unless Rosh HaShana falls out on Monday or Tuesday, in which case, Ashkenazim start from two Sundays before Rosh HaShana. Mishna Brurah 581:6 explains that the reason that the preparation is no less than four days is because some had the custom to fast for ten days prior to Yom Kippur, however, since one can’t fast on Rosh HaShana’s two days, Shabbat Shuvah, and Erev Yom Kippur, one had to begin fasting four days prior to Rosh HaShana (see there for other reasons).
- Kaf HaChaim 581:1,2, and Maamer Mordechai (Rav Mordechai Eliyahu) 34:4 hold that one should only say Selichot after Chatzot and if one had a minhag to say it earlier one should change the minhag.
- Mishna Brurah’s introduction to 581, Maamer Mordechai (Rav Mordechai Eliyahu) 34:5 write that preferably, Selichot should be said at the end of the night before Olot HaShachar.
- Maamer Mordechai 34:5.
- Maamer Mordechai 34:5
- Mishna Brurah 581:2 says that the Minhag Ashkenaz is to say LeDavid Hashem Ori after Shacharit from Rosh Chodesh Elul until and including Shemini Aseret. LeDavid Hashem Ori should be said after Shir Shel Yom. On days when there’s Mussaf, LeDavid Hashem Ori is said before Ein Chamocha. On Rosh Chodesh, Barchei Nafsei is said before LeDavid Hashem Ori. Sh”t Shevet HaLevi 10:67 and Chazon Ovadyah (pg 24) writes that in Israel the minhag is to say it until and including Hoshana Rabba.
- Rav Ovadyah (Chazon Ovadyah pg 24) writes that even for sephardim it’s proper to say LeDavid Hashem after shacharit.
- Mateh Efraim 551:6 writes that LeDavid Hashem Ori in the evening should be said after Mincha. So rules Mishna Brurah 581:2. However, Elef HaMagen 581:10 holds that LeDavid Hashem Ori should be said after Mariv. Shalmei Moed (pg 21) in name of Rav Shlomo Zalman writes that one should follow the minhag of the Tzibbur one is praying with. Shalmei Moed (pg 21) says that the minhag Ashkenaz is to say LeDavid Hashem Ori after Mariv (such is how the Artscroll Siddur has it).
- Rama 581:1 writes that one should begin blowing the Shofar from Rosh Chodesh Elul. Mishna Brurah 581:3 writes that some start on the first day of Rosh Chodesh and some start from the second day of Rosh Chodesh.
- Mishna Brurah 581:6 writes that the Levush says that the Shliach Tzibbur should wear a Talit during Selichot but not make a Bracha since there’s a dispute if one can fulfill Tzitzit at night. However, the Taz argues that one shouldn’t enter himself into a dispute (whether to make a Bracha) and so one should rather borrow a Talit from a friend and have Kavana not to acquire it but to use it for respect.
- Rama 581:1
- Rama 581:1
- Mishna Brurah 581:13
- Mishna Brurah 8:24 writes that for sure one should make the Bracha of Talit and cover the Tzitzit rather than make a Bracha on Tzitzit and then on Talit. Even if there will be a long time between putting on the Tzitzit and wearing the Talit, one should still say only one Bracha on the Talit because there are many concerns about making the Bracha on the Tzitzit (it may not be split on the sides a majority, it may not fit the proper Shuir, or one may have slept in the Tzitzit). [this is also brought in Yalkut Yosef (Tzitzit pg 294, Kitzur S”A 16:2).] Siach Halacha 8:47 writes that if one does put on Tzitzit a long time before Talit and one covers all the concerns (the Tzitzit is split on the sides, it is the proper size, and one didn’t sleep in them) then one should make the Bracha on Tzitzit and then later on the Talit. (This is only fathomable if one puts on the Tzitzit and makes the Bracha after Olot HaShachar as is clear in 18:3 and still there will be a break between then and when one puts on a Talit.) However, the Shalmei Moed (pg 22) brings Rav Shlomo Zalman Aurerbach who argues that the Mishna Brurah meant that no matter whether it’s a long time or not, one does not make a two Brachot.
- Minchat Shlomo 4:1:3 writes that regarding Selichot a bachur who doesn’t wear a Talit should be careful to make the Bracha on Tzitzit right after Olot after feeling the Tzitzit. This is based on the Rama 18:3 who writes that if one put on a Talit Katan before Olot HaShachar, then, at Olot one should feel the strings of the Tzitzit and make a Bracha.