Halacha requires that before making a Bracha over the Tzitzis, one must check the Tzitzis strings every day to ensure that they have not broken in a way that would render them Pasul and make the Bracha a Bracha Levatala. One should check the strings, the windings and where the strings are inserted and tied into the garment. One must also separate the strings so that they are not tangled. The Alter Rebbe rules that the Tzitzis should also be checked on Shabbos.
For a Tallis Gadol, this is done before making the Bracha while the Tallis is draped over their right shoulder. One should also remember to check the Tallis Katan strings. Since those who wear a Tallis Gadol do not make a Bracha on the Tallis Katan, it is easy to forget to check them. It is advisable to make a point of checking their Tallis Katan strings at the same time as they check the Tallis Gadol, so that they do not forget.
For Bochurim who make a Bracha on the Tallis Katan, this should be done before making the Bracha.
