One must avoid taking trips on Tish’a B’Av, because they divert one’s attention from mourning. One should also avoid friendly conversations, because they can lead to laughter and lightheadedness (Sh.A. 554:21). It is a good practice to talk about the churban, Israel’s tribulations, and the ways of repentance for both the community and the individual.
Even those who are accustomed to visiting cemeteries after the recitation of Kinot must be careful not to go in large groups, because they might become distracted from mourning (Rama 559:10, M.B. 41).
It is obvious that one should not refrain from going to the Kotel out of concern that he might meet friends there and be happy. I heard from my father, my teacher, that there is no greater rectification for Tish’a B’Av than going to the Western Wall – the only remnant [of our Temple] left standing after the churban – and praying for the Beit HaMikdash to be rebuilt speedily in our days. On the contrary, the fact that many people assemble there increases the power of the prayers and magnifies God’s glory. My father added that just as one would not say that it is forbidden to build the Holy Temple during the Nine Days because it is an act of building that entails joy, so too one should not say that it is forbidden to visit the Kotel on Tish’a B’Av for fear that one might meet friends there. Rather, if one meets his friends there, he should avoid saying Shalom, but he may shake their hands lovingly and pray with them for the rebuilding of the Beit HaMikdash.