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As an expression of mourning, we do not greet people or send them gifts on Tisha Be-Av. Shaking hands is permitted, as is taking an interest in how someone is doing, but too much chatting should be avoided because it is likely to detract from the fast.
On the night of Tisha Be-Av, it is customary to turn off some of the lights in the synagogue. Doing so at home is appropriate as well. Some sleep without a pillow or put their mattress on the floor and sleep there.
Just as a mourner may not study Torah during shiva because Torah study is enjoyable (14:9 above), so too we do not study Torah on Tisha Be-Av. However, it is permissible to study sad subjects and the depressing parts of Jewish history, as this is appropriate to the spirit of the day. One can also study the laws pertaining to Tisha Be-Av and to mourning in general. One should not read newspapers and interesting books, as material not connected to Tisha Be-Av is likely to distract from mourning and fasting. For the same reason, people should not go to work on Tisha Be-Av. However, if that will cause a serious loss, one may work. While commerce in general should be avoided on Tisha Be-Av, food products may be sold.
From the start of Tisha Be-Av until the afternoon, it is customary to sit on something low. People who find this difficult may sit in regular chairs. From midday, everyone may sit in regular chairs.
