You must tear four vertical inches at the neck of your shirt (and jacket, too, if you wear one) when seeing the ruins of the Temple in Jerusalem for the first time in more than 30 days. You do not need to be close by; do kri'a even if you see the mosques that are on top of the Temple mount.

Hoshanot were done in the Temple in Jerusalem and the community is required to do hoshanot. Individuals are not required to join, but it is the proper practice to join if holding a lulav and etrog.

A glass is broken in commemoration of the destruction of the Temple.
 

It is forbidden to enter into places of idol worship, such as a Buddhist or other temple of eastern religions.
 

It is no longer customary to leave part of a house unfinished (as a remembrance of the Jerusalem Temple's destruction) and it is not necessary to wreck part of a completed house.
 

It is a non-binding custom to braid challa as a reminder of the 12 showbreads (lechem ha'panim) in the Temple that were changed each Shabbat. Proper practice is to braid each challa from six pieces of dough, as there were two columns of six loaves each.
Note Since these showbreads were not changed on Rosh Hashana and Jewish festivals, we may use round challot for those holidays (unless they fall on Shabbat or the holiday is Passover!).

There are many opinions as to why we read hallel at night: most are related either to praising God for saving the Jewish people or to accompanying the Passover sacrifice in the Temple in Jerusalem.

You must separate a small portion of dough for the cohanim/priests whenever you make bread, rolls, or pizza of the Five Grains in certain quantities. This separated portion is called “challa.”
Note Since there is no Temple at present, we burn the portion of dough.
The requirement to separate challa applies to dough baked at home or commercially (such as a pizza shop), whether for eating on weekdays or for Shabbat/Jewish festivals. For more details, see Challa.
 

Rosh Hashana is the beginning of the Jewish calendar year (there are three other dates that begin other aspects of the Jewish year).
Rosh Hashana is observed for two days, which are considered to be one continuous day. In Temple times, a cohen would offer a sacrifice but might not know until the following evening, after the new moon had been seen (or not), whether he had offered the Rosh Hashana offering.
Rosh Hashana focuses on the idea of God as King and of our relationship as Jews to that King.

Men and women should be separated during prayer services with a mechitza that blocks the men's view of the women. The goal is to keep the men and women from distracting each other during prayer. This idea originated in the Temple in Jerusalem.

The limits of kilayim keep:

• Individual creations true to themselves, in the way they were created by God, and
• Different, or opposing, spiritual forces governing creation in their own places and within their own bounds.

In the holiness of the Tabernacle or Temple, where opposites were peaceably and constructively resolved, kilayim in the form of sha'atnez was not only permitted but formed the foundation of all main tapestries and two of the High Priest's garments. Kilayim-type laws apply today to:

• Animals (not yoking an ox and donkey together; not interbreeding, say, a horse and a donkey to produce a mule),
• Food (not eating milk with meat),
• Clothing - not wearing a garment made of a mixture of linen and wool (sha'atnez), and
• Plants (interplanting, interbreeding, and grafting different species).
  Note Vineyards in Eretz Yisrael may only be near fruit trees if:
  1. A wall divides fruit tree and vineyard, OR
  2. The vineyard is not a bona fide vineyard. A bona fide vineyard has at least 5 grapevines in at least two rows, with at least two vines in one row and three in the other. 

Omer is counted for 49 days, from the second day of Passover to the day before Shavuot.  Omer connects the two holidays both physically and spiritually.  In Biblical times, an omer (a specific measure of volume) of barley was brought as an offering to the Temple in Jerusalem on the second day of Passover.  Once the barley offering had been brought, all grain changed status from “chadash” to “yashan” and could be eaten.
Due to tragedies that occurred during the omer period, especially the death of 24,000 students of Rabbi Akiva during the second century, we observe a semi-mourning period during 33 days of the 49 days of the omer.

Although challa refers to the two loaves of bread (or matza) over which we say the ha'motzi blessing at Shabbat and Jewish festival meals, challa also means the portion of dough or bread that we are obligated to give to the cohen/priests during Temple times.  Today, we burn a token portion (“challa”) of dough.

Almost all mitzvot may be enhanced by:

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

Jewish Festivals are listed in the Torah and are of two types: 

1. Three pilgrimage festivals (shalosh regalim):

• Passover,
• Shavuot, and
• Sukkot (including Shimini Atzeret).

These festivals were celebrated in ancient times by "appearing before God"--by bringing offerings to the Tabernacle or Temple.

2. High Holidays: 

• The Jewish New Year (Rosh Hashana—“Yom Teru'a” in the Torah), and the
• Day of Atonement (Yom Kippur).

 
Duration
Jewish holidays that were originally one day are now observed as follows:

• Rosh Hashana--2 days.
• Yom Kippur--1 day.
• Shavuot--1 day in Eretz Yisrael or 2 days elsewhere.
• Passover has festival days at the beginning and end of the holiday and intermediary days of lesser holiness, which are called chol ha'moed. In Eretz Yisrael, Passover lasts for 7 days in total and the first and last days are festival days. Outside of Eretz Yisrael, Passover lasts 8 days and has two festival days at the beginning and two at the end.
• Sukkot has festival days at the beginning and at the end and intermediary days of lesser holiness, which are called chol ha'moed. In Eretz Yisrael, Sukkot lasts for 8 days and the first and last days are festival days (the last day is Shimini Atzeret). Outside of Eretz Yisrael, Sukkot lasts for 9 days and the first two days and last days are festival days (the 8th day is Shimini Atzeret and the 9th day is Simchat Torah).

Character
Each holiday contributes its own character to Jewish life (Passover--the theme of freedom; Yom Kippur brings atonement, etc.). 

Celebrating
How to celebrate these holidays is detailed in our Oral Law and halacha books. Jewish festivals as practiced today are similar in holiness to Shabbat. As with Shabbat, the Jewish festival has candle lighting, kiddush at two meals, and havdala.   We eat our best food and wear our best clothing on Jewish festivals (we eat our next-best food and wear our next-best clothing on Shabbat!).
The main idea behind eating meals on Jewish festivals is joy (simcha), so you should drink wine and eat meat (only if you enjoy wine and meat).  There is no third meal on Jewish festivals since people used to eat two meals each day (adding a third meal on Shabbat was for enjoyment/oneg).
 
Melachot
Any activities or actions permitted on Shabbat are also permitted on the Jewish festivals. Actions that are forbidden on Shabbat are generally also forbidden on Jewish festivals, but there are some leniencies (only if the actions are needed for that festival day).
Examples

• Lighting from an existing flame,
• Cooking and baking for the Jewish festival day, and
• Carrying outside the eruv (hotza'a--transferring objects between domains).

 
Grama
Grama (indirectly causing an action) is permitted on Jewish festivals (but not on Shabbat). For example, you may advance or delay a timer that will make a light go on or off in the future (the timer must already be plugged in and operating from before sunset of the festival day).
Note For an action to be considered indirect based on time, there must be at least 2.5 seconds after the first action is done before the resulting action begins to happen.

Psik Reisha Dla Neicha Lei
Psik reisha dla neicha lei is forbidden on Jewish festivals, just as it is on Shabbat.

D'oraita Restrictions
D'oraita restrictions apply world-wide to:

• First and seventh days of Passover,
• First and eighth days of Sukkot,
• First day of Shavuot,
• Yom Kippur,
• First day of Rosh Hashana.

Note The same restrictions apply to all other Jewish festival days but are rabbinical.
 
Women
In general, women are not required to perform the positive, time-dependent commandments. Women and girls are not required to eat any Jewish festival meals except the Passover seder meal (but they are not allowed to fast on those days).