That is why on Tish'a BeAb it is not recommended to work. Working will divert our minds from the feeling of grief. Refraining from work on Tisha BeAb, however, is not an formal prohibition, but rather optional, depending ultimately on one's family tradition, and one's financial and professional situation.
LIMUD TORAH: On Tish'a BeAb we don't study Torah, because studying Torah is considered a pleasurable activity. We only read and study books or texts with a 'sad' content such as the book of Iyov or Ekha, Josephus Flavious, etc.
TEFILIN: We do not use Tefilin in the morning. The Tefilin is a signal of 'honor', a crown in our heads which declares that we are the people of God. In our community we use our Talit and Tefilin for Mincha. In Yerushalaim, the Sepharadic Minhag is to wear Talit and Tefilin privately, before one goes to the Synagogue and say the Shema Israel at home with Talit and Tefilin.
SHE-ELAT SHALOM: We don't greet each other as usual, because our mood is a mourner's mood.
SITTING ON THE FLOOR: Many communities have the custom that during the reading of Megilat Ekha people don't sit on the Synagogue's benches but on the floor, while the lights are dimmed, also as an indication of mourning.
Our Chakhamim assured us that those who cried for the destruction of Yerushalaim will have the merit to rejoice with the reconstruction of Yerushalaim, B'H soon, in our days!
Click HERE to watch a special clip on Tish'a beAb by Rabbi Berel Wein.
Read HERE and article by Rabbi Soloveitchik on happiness and mourning.