1. It is customary not to make a wedding during the Three Weeks, even without a festive meal.

2. Dancing is prohibited, even without music, during the Three Weeks (for Sephardim and Ashkenazim).

This law is emphasized by Rabbi Ovadiah Yosef in a letter written to Rabbi Isaac Dweck.

“To my esteemed and beloved friend, מיחדי סגולה ( a distinguished individual), a man of יראת שמים (God-fearing), Rabbi Isaac Dweck, שליט"א ,Rabbi for the Deal, NJ Congregation … Regarding what you have asked me about dancing during the Three Weeks, I would like to answer you that it is prohibited without question, both during the week and Saturday night, the entire three week period. This halachah applies to both Sephardim and Ashkenazim. This law is brought down in the Magen Abraham, Aliah Rabbah, Prei Megadim, Kaf Hahaim … and many others. It is clear from the Poskim that the prohibition starts from the seventeenth day of Tammuz through Tishah B’Av, and these days are called בין המצרים ... It is also brought in the Midrash of Eichah that during this period thousands of our brethren have been killed and died in famine in the period of the destruction of the first and the second Temple. Therefore these are days of tragedy and mourning for the Jewish nation…

“This prohibition also applies to separate dancing even with a separating divider. Additionally, mixed dancing is prohibited without question the whole year, as it is brought down in many Poskim…

The common claim people set forth that mixed dancing is necessary for marriage is wrong, and it is the argument of the יצר הרע (evil inclination), because Hashem has many other avenues available for people to find their spouse.”

3. a. Music is forbidden because it leads to joy. No distinction is made between live music at a party or music from a radio or tape, even listened to in private. This ban is upheld by Rabbi Ovadiah Yosef and Rabbi Moshe Feinstein, zt”l.

b. Group singing should not be engaged in (e.g. in camp) but singing to Hashem, i.e. during prayer, is permitted.

c. One who earns his livelihood in the music field is permitted to work until Rosh Hodesh Av. However, on the seventeenth of Tammuz and from Rosh Hodesh (including Rosh Hodesh) till Tishah B’Av he should refrain from doing so.

4. We do not recite the berachah of שהחיינו during the Three Weeks because it is not appropriate to say שהחיינו לזמן הזה, that Hashem granted us life, sustained us and let us reach this time, if this is a time of tragedy and mourning. 

a. Therefore, anything requiring the berachah of שהחיינו should not be enjoyed during this period — i.e. new clothing or new fruit. 

b. One can be lenient regarding this prohibition on Shabbat — however, wearing new clothes during the Nine Days is prohibited even on Shabbat.

c. Since a Brit Milah or Pidyon HaBen that occurs during this peroid is a time-related mitzvah, we recite the שהחיינו on these occasions

d. If a person already recited the berachah over a new fruit then he should say שהחיינו before he eats it.

e. If he did not say שהחיינו then he should wait until after the Tenth of Av, then take another new fruit and recite שהחיינו ,keeping in mind the new fruit that he already ate during the Three Weeks.

f. A minor child who cannot make a distinction between the Three Weeks and the rest of the year should recite שהחיינו when he eats a new fruit, so as not to mistakenly omit שהחיינו at other times. 

5. Since the Three Weeks is a time of trouble we must avoid as much as possible anything that is potentially dangerous. Included in this is hitting children — one should refrain from this type of punishment.

6. a. According to our custom there is no prohibition regarding haircutting or shaving, except during the week of Tishah B’Av.

b. A Sephardi living among Ashkenazim does not have to accept upon himself the stringency of not shaving or cutting his hair, according to the letter of the law. However, it is preferable to be strict and follow the Ashkenazic custom. He should be sure to state explicitly that he is doing so בלי נדר  (not promising to keep the custom) so he will not be obligated in nullification of vows  (התרת נדרים).