22:7 Tachanun is not said if a groom is present in shul the entire week of his sheva brachos. This is the case if it is a first marriage for either partner but if it is a second (or later) marriage for both of them, then Tachanun is only not recited for three days. On the wedding day itself, Tachanun is said at shacharis but not at mincha, which is close to the ceremony. (There are opinions that Tachanun should also be omitted at shacharis – see Mishnah Brurah 131:21.)

22:8 Tachanun is also not said on the following days: Rosh Chodesh, 15 Av, 15 Shvat, Chanukah, Purim (including Shushan Purim), Purim Katan (both days), Lag b'Omer, the entire month of Nisan, Tisha b'Av, the days between Yom Kippur and Succos, from Rosh Chodesh Sivan through the day after Shavuos, and the day after Succos. On all these days, Tachanun is also not recited at mincha on the day before. However, Tachanun is said at mincha on the day before Rosh Hashana and the day before Yom Kippur. (Mishnah Brurah disagrees - see MB 581:22 and MB 604:3, respectively.) On the day before Rosh Hashana, selichos are recited before shacharis but Tachanun is not said after selichos as it usually is. (Some don’t say Tachanun for six days after Shavuos – MB 131:36.)