1) During these three weeks one may not hit children or students even very lightly, as it is dangerous. (Shulchan aruch and Kaf Hachaim 551)

2) On the three Shabbassos which occur during these three weeks we do not read a Haftarah which is relevant to the Parshah of the week. Instead, we read Haftarot which are from the rebukes of the prophets before the destruction of the temple. These are called the “three of punishment”. They are “the words of yirmiyah”, “Listen to the word of Hashem”and “The vision of Yeshayahu”. (Kitzur 122)

1)    During these three weeks one should refrain from indulging in outings, and especially in dangerous places. (Setei Chemed, Mahara”ch Palaji)

2)    During these days one should increase love of other Jews and other interactions with one’s fellows, to repair the sin of baseless hatred, which was the cause of the destruction of the temple. (Latter authorities)