The Rebbe's guidance on tefillin, tefillin of Rabbeinu Tam, and tzitzis:
Tefillin every day. Putting on tefillin daily connects a Jew deeply with G-d and brings a daily liberation of the spirit (IK 9482). Tefillin bring special protection, notably for soldiers (IK 1496, 10631). Encourage young people and newcomers to put on tefillin with patience and persistence (IK 1301, 6209, 7684). A boy begins putting on tefillin two months before his bar mitzvah (IK 6082, 7134); on when Chol HaMoed falls within those two months, see IK 8755. For checking tefillin, see Health – Checking tefillin and mezuzos.
Tefillin of Rabbeinu Tam. Wearing Rabbeinu Tam tefillin is very important (IK 6226, 10373), with both awe and joy (IK 8798). It is good to begin around one's birthday or at engagement (IK 2279, 632, 650, 2210), though in some cases the Rebbe advised waiting and preparing spiritually first (IK 2084). Don't miss a day once begun (IK 3058), and don't stop a longstanding practice (IK 8368). Strive for purity in putting them on (IK 5794), and learn both their laws and the related Chassidus (IK 5761, 9047). On tefillin of Shimusha Rabba and the Raavad, see IK 1338.
Tzitzis. The mitzvah of tzitzis applies continuously while one wears them; every moment counts (IK 2619), and a single mitzvah of a Jew exceeds the service of the angels (IK 392). The mitzvah of tzitzis brings merit for health and long life (IK 3578, 1093). Beautifying tzitzis, as the Alter Rebbe taught, is part of the mitzvah itself (IK 9426, 5098). Machine-made strings are permitted if made with proper intent, but should not be promoted as ideal, and stringencies should not be publicized as binding (IK 407, 1722, 1800, 4682); proper intent and manual effort matter in making them (IK 1665). On sleeping in a tallis katan, see IK 4302, 6917; on the placement of the holes, see IK 342.
See also: Health – Checking tefillin and mezuzos; Parenting – Bar and bas mitzvah; Jewish outreach – Mitzvah campaigns.