After Uva Letzion, Mizmor 86 (“Tefila LeDavid”) and the verses of Bet Ya’akov arerecited. The Seder Hayom, the Avudraham and the Tur all discuss Mizmor 86 and say that it was instituted because in it, we ask Hashem to answer all our prayers. Additionally, they mention that one should be careful to recite it and to not treat it lightly. Rabbi Haim Palagi (Kaf HaHaim Palagi 17:14) notes that the psalm has 186 words, which equals the numerical value of “Makom”, or Hashem’s omnipresence, and thus one should have great concentration during its recital. Furthermore, the sum of the products of the value of each letter in Hashem’s four-letter Name, Yud-Ke-Vav-Ke(10×10+5×5+6×6+5×5), is also 186.
Interestingly, according to the Sephardic custom, on days that Tahanun is omitted,Tefila LeDavid is also omitted. Rabbi Simha Rabinowitz (Piske Teshuvot § 132) explains this by saying that the psalm says “Beyom Tzrati Ekraeka” (lit. “on the day of my distress I shall call You”), which refers to days on which Tahanun is said. According to Nusach Sfard, there are days when Tahanun is not recited but Tefila LeDavid isrecited, such as when a groom is present.
Summary: One should recite Mizmor 86 with intent concentration. It is notrecited on days that Tahanun is omitted.