Yizkor is not required to be said at all, but it is the custom in most places. Yizkor is normally said on Yom Kippur (and the final day of Passover, the second day of Shavuot and on Shmini Atzeret), when many people attend the synagogue prayer services.
Yizkor may be said anytime you wish—even when it is not a Jewish festival--and does not require a minyan.

A mourner (avel) is permitted to say she'hecheyanu for himself but should not say she'hecheyanu if required for the congregation.  An avel should say she'hecheyanu on:

• Eating a “new” fruit.
• Wearing a new garment.
• Lighting Chanuka candles at home for the first time that year.

 An avel should not do the following, since he should not say she'hecheyanu unless it is necessary:

• Light Chanuka candles in synagogue.
• Read the megila.
• Blow shofar on Rosh Hashana.

The following must each hear or say havdala for themselves:

• Men and boys 13 years old and up, and
• Women and girls 12 years old and up.

All Jews, both men and women, must fulfill the commandment to remember what Amaleik did to the Israelites. The paragraph about that episode, called Parashat Zachor (found in Parashat Ki Teitzei:  Deuteronomy/Devarim 25:17-19) is read on the Shabbat morning before Purim as a law established by Chazal (takana). The commandment is fulfilled whenever that episode in the Torah is read, even privately and at home, but there is special value in hearing it read in a synagogue on that Shabbat preceding Purim.

You may not light Jewish festival (or Shabbat) candles before plag ha'mincha.  The candles must burn until at least dark (tzeit ha'kochavim) and someone must be there to see the light from the candles after dark.
SITUATION  Mincha minyan begins at plag ha'mincha. You cannot light candles at home and still get to mincha minyan on time.
WHAT TO DO You may light a candle without a blessing, just so you can have a flame for after the festival has begun. You go to synagogue and after ma'ariv you return home and light the candles from the flame which was burning from before sunset. If you will not have a flame burning from before sunset, you must say mincha on your own (anytime from half an hour after mid-day until sunset). You will light candles after plag ha'mincha but before sunset and not join the mincha minyan. Women should skip mincha and light candles either 18 minutes before sunset or have a flame burning from before sunset and light candles from that flame once the festival has begun (but she may not light from a new flame or a match).

Shabbat begins for women when they light the Shabbat candles or at sunset, whichever is earlier.

These holy writings (tashmishei kedusha) may not be thrown directly into the trash, but should ideally be buried with like items (sheimot):

• Holy writings that contain God's name.
• Parts of Tanach (24-book Jewish Bible).
• Explanations of the Torah or commandments.

However, if a printed or written page (in contrast to parchment scrolls such as tefilin, Torahs, or mezuzas) contains God's name plus secular content, it must be double wrapped in plastic before being thrown in the trash.
Do not throw into trash, even if double wrapped:

• Handwritten scrolls of Torah, tefilin, mezuza.
• Printed Torah, Talmud, siddur, books of halacha, or Torah commentaries.

Rather, put them into a sheimot collection box or wrap in plastic and bury in a place where they will not be dug up. It does not need to be a cemetery.

Double wrap and throw into trash:

• Newspapers and flyers that have Torah psukim or Torah commentaries and also have non-Torah content.
  Reason Non-Torah material should not be buried as sheimot. 
• Children's school handouts with psukim from the Torah or halachot that also contain non-Torah content (if they ONLY contain words of Torah, they should be buried as sheimot).

For disposal of items used for mitzvot (tashmishei mitzva), you may wrap in one layer of plastic and throw it in normal garbage:

• Lulav,
• Etrog, or
• Talit/tzitzit (but NOT tefilin!)

There are many approaches as to when to start Shabbat:

Men
For men, whichever is first:

• At sunset, or
• When they light candles intending to begin Shabbat then, or
• When they say Mizmor shir l'yom haShabbat.

Women
For women, whichever is first:

• When they light candles intending to begin Shabbat then (most people light 18 minutes before sunset but local customs can vary; e.g., Jerusalem), or
• In case of urgent need, just before sunset if they have not lit candles.

 
Note Even if a husband has finished ma'ariv for Shabbat, his wife is not required to start Shabbat when he does, and she may still light her candles at the normal candle lighting time. The husband does not need to wait outside until she has lit. However, the ideal situation is for the home to be ready (including table set) by the time the husband has finished ma'ariv and has returned home from synagogue.
 
Community-Wide Considerations

• If an entire community begins Shabbat at any time earlier than sunset on Friday, EVERYONE must begin Shabbat at that time.
   
• If there are at least two minyans in any community, no one is required to start Shabbat with the earliest one (but if you associate yourself with one of those minyans, you must follow their custom).

Lashon ha'ra is saying (or communicating in any way--even by rolling your eyes, winking, etc.) anything derogatory or negative about someone that can hurt him or her in any way--by causing embarrassment, loss of money, lowered esteem, bad reputation, etc. 
 
Lashon ha'ra in which you attribute the negative statement about the person to whom you are speaking to someone else is called rechilut (gossip). 
 
Lashon ha'ra that is false is called motzi shem ra. Saying something that is true is not lashon ha'ra if it is being said for a positive purpose (even though the same words would be lashon ha'ra if they were only intended to hurt another person and had no positive purpose).
 
Lashon ha'ra, including rechilut, is forbidden to be said about shomer Shabbat Jews except for a positive purpose; motzi shem ra is forbidden to say about anyone--Jewish or not, shomer Shabbat or not, whether for a positive purpose or not.
 
Speaking Lashon HaRa
 
When You May Say Lashon HaRa
Lashon ha'ra, including rechilut, even if truthful, is not permitted except for a constructive or positive purpose. (Motzi shem ra is never permitted.) Its purpose cannot be to hurt a person.  It is permitted and recommended to tell the facts about someone:

1. To protect others from being hurt (being cheated, molested, etc.), or
2.  For a positive purpose that cannot be achieved through any other means.

 
Lashon HaRa To Protect Others from Being Hurt
You may say truthful lashon ha'ra (including rechilut, if it is necessary to divulge the name of the person who told you):

• To prevent a bad person from telling children bad things or to keep children from learning bad behavior from the bad person;
• To avoid being implicated in what the bad person is doing;

• To prevent other Jews' suffering a loss by using a worker who did bad work for you.

• If a businessman cheats you or lies to you, you should warn other Jews about him (but only if you suspect they want to do business with him).
• If you know something bad about someone who a third person wants to date or marry, in many cases you are required to tell what you know (but this can be very complicated and dangerous and a rabbi should be consulted about what to do in many cases)!

 
When You May Add Facts to Correct Possible Lashon HaRa
If the reasons behind an action are not clear and someone may get the wrong/negative impression of someone in question, then you should tell the facts and tell the entire story. 
Example
Someone (A) insults another person (B) in public. Entire story is that B beat up A previously. Knowing the full story changes how people might view A.
Note If it is only your opinion, state that instead of declaring it as fact.
 
Lashon HaRa To Allow Gain
Saying lashon ha'ra for a positive purpose includes gain for yourself or for someone else; you may talk about others in cases such as these:

• Psychotherapy  You may say truthful lashon ha'ra or rechilut to a psychotherapist since you don't know what is important. Outside of therapy and with non-therapists, you may say anything that will bring about a positive result (and only if there is no other way to achieve that result).

   

• Upset  If you are upset by what a person did to you and it will help you to calm down by telling what was done to you (that is, you will gain by feeling better).

 
Note If you want to ask someone for information that could be lashon ha'ra, you should say why you are asking so the other person will understand that it is for a positive purpose and is therefore not lashon ha'ra.
 
 
Lashon HaRa and Specific Cases
 
Children, Shomer Shabbat Person, Groups
Even truthful lashon ha'ra, including rechilut, may not be said about a Jewish child or a shomer Shabbat person or group of people unless for a positive purpose that cannot be achieved any other way.

• A parent should not rebuke or criticize a child if it will embarrass the child in front of others.
• A child (whether young or adult) may not correct a parent who is saying lashon ha'ra, unless the parent would want to be reminded that the parent is saying lashon ha'ra. Even then, it must be done respectfully. 
• You may make statements about groups of people in general, even if negative, as long as the purpose is to protect other people from them. But what you say must be true.   

 
Lashon HaRa: Public Knowledge
You may mention information that is public knowledge. But your intent should not be to spread the word, but rather just to pass along interesting information.
Example
Saying, “Did you hear that the president of the synagogue just got convicted of...”
 
Lashon HaRa: Mass Media
You may read in the paper, see on TV, or hear on the radio an account of someone's bad behavior (since you cannot know whether it will affect you or be important for you to know until you read or hear the information, it may be OK; ask a rabbi). You may not accept it as being the complete truth, but you should be wary.
 
Lashon HaRa: Shomer Shabbat Public Figure
You may not tell or listen to lashon ha'ra about a public figure who is a shomer Shabbat Jew unless there is a purpose.
You may give your opinion about a shomer Shabbat politician as long as you state it as your opinion and as long as giving your opinion may help other people.
 
Lashon HaRa: Shomer Shabbat Organization
You may not say any of the three types of speaking ill about an organization, school, synagogue, etc., whose members or employees are shomer Shabbat--except for a positive purpose.
Examples
You may not say any of the three types of lashon ha'ra about a Jewish school's cost, bad teachers, etc., unless it may be relevant to future students (and even if it is relevant, you may still not say motzi shem ra).
You may not say, “I don't like that shul because there is lots of talking,” unless you think the person will appreciate knowing since he or she will not want to go to a shul with lots of talking.
 
Lashon HaRa: Asked for Opinion
If you are asked for your opinion, you may give it if it is relevant (has a useful purpose) to the person asking. Otherwise, no comment.
 
If you are asked your opinion about a Torah lecture or lecturer, you may give your opinion only AS your opinion, not as criticism.
 
Lashon HaRa: Told in Confidence
If you have been told something in confidence, even if you think it is best for the person who told you if you pass it along, you may still not re-tell anyone else. You may say, “I cannot speak about that” if you are asked. Consult a rabbi.
 
Lashon HaRa: Getting Back at Someone
If someone hurts you, you may get back at the person at the time of the action against you.  But afterward, it would be revenge and is forbidden.
Example
Someone tells you, “You are good for nothing.” You may say, “You are worse than I am,” if it makes you feel better.
 
Lashon HaRa: Bet Din Summons
If someone with whom you have a problem refuses a hazmana (summons) from a bet din, you may publicize a letter from the bet din saying the person refused the hazmana so that the recipient might agree to go to the bet din due to public embarrassment.
 
Lashon HaRa: Bet Din for Abuse
All matters between Jews should, ideally, initially go to bet din but only if the bet din is capable of resolving the problem. In cases of suspected child or spousal (or other) abuse, you may report it to the police if there is no bet din that is capable of dealing with the problem immediately: You are not required to wait while a bet din gets around to your case. The key is to expedite the case.
Note Some cities have special batei din for such matters.
Note Beware of governmental agencies that may take away children from their homes, even without evidence.
 
Listening to and Believing Lashon HaRa
Listening to and believing any category of lashon ha'ra is also forbidden. If you do hear something bad about someone else, do not believe that it is definitely true--but you may believe that it might be true. When you hear lashon ha'ra:

• You can try to change the subject, since pointing out that lashon ha'ra is being said may not stop it from being said.
• If you see a shomer Shabbat Jew doing something that seems to be forbidden, you should judge him/her favorably and assume that there is a good interpretation to what is being done.

Example
Situation
You see someone who is not shomer mitzvot get in a car on Shabbat.
What To Do
Make the logical assumption that he/she is going to drive (and not for a halachically permissible purpose).
Situation
You see a shomer Shabbat person get in a car on Shabbat.
What To Do
Assume there is a good, halachic reason for it. However, you may not ignore reality or make implausible or unlikely excuses for bad behavior.

Only buildings in which people live need a mezuza, so you do not need to put them on offices, synagogues, or stores (unless people also live there). No mezuza is needed on an eruv.

The ideal time and way to count the omer is to wait until dark, stand up, say the blessing, and then count the omer for that day.
SITUATION You want to count the omer before dark (as is often done in synagogues at the end of ma'ariv).
STATUSSince the correct practice is to count the omer after dark, you should:

• Count again with a blessing sometime after dark, or else 
• Count during the following day (but before sunset) without a blessing.

WHAT TO DO  Do the counting without saying the blessing and make a condition (mentally or verbally, either is OK) that if you remember to count the omer again after dark, the first time you counted, does not count (!) Then, if you do remember after dark, say the blessing and count the omer for that day a second time.

 

On Shabbat, even though you may cause a compressor to turn on while you are using it or soon afterward, you may:

• Open the door to a refrigerator or freezer.
• Use a water cooler.

Almost all mitzvot may be enhanced by:

• Making them beautiful (hidur mitzva), or
• Observing non-required stringencies (mehadrin).