The Rebbe's guidance for when learning is hard — no motivation, laziness, feeling stuck — and on study partners:
Lack of motivation is an illusion. Feeling unmotivated or unable to learn is a tactic of the yetzer hara; recognize it, take responsibility for yourself and keep learning (IK 3206, 4137, 5846). Feelings of inferiority about one's abilities are unfounded (IK 3623). The real obstacles are inner, not the place or the circumstances (IK 5753). Everyone has free choice and G-d-given strength to overcome (IK 4538).
Against laziness. Study Tanya chapter 41 — even grasping its basic meaning drives away inertia (IK 3668); learning passages of Tanya by heart and contemplating G-d's presence help too (IK 4153, 6711, 7235).
Effort, step by step. Success in learning comes through real effort suited to one's own strengths (IK 2882, 9608, 10228). Progress is gradual; don't expect miracles (IK 1941, 8872). Discipline and following one's mentor's guidance come first (IK 2677, 4358, 10228). A student's task is steady learning, not hunting for questions or novelties (IK 3787, 5486).
Keep the fire. Without Chassidus, learning and mitzvos grow cold; Chassidus brings vitality (IK 2645, 8721). Learn where your heart is drawn, which brings greater diligence (IK 9075). Rather than changing your schedule mid-year, add enthusiasm to it (IK 8594). Healthy competition among learners spurs diligence (IK 6270, 6658), and your growth shouldn't depend on others' attitudes (IK 4477). Time is precious — don't waste it (IK 2445, 7211).
A study partner. Learning with a partner gives encouragement and accountability; set realistic goals (IK 5004, 4287). Arranging an older study partner for a student is normal, not embarrassing (IK 10222). Balance broad review (girsa) and in-depth study (iyun) according to your nature, alone or with a partner (IK 3563). When learning alone, persist and understanding will come (IK 3554, 4545); on one's own, first complete Shnayim Mikra and then learn Chassidus (IK 7368). If Tanya is hard at first, begin with Iggeres HaTeshuvah (IK 7443).
See also: Torah study – Learning by heart and memory; Torah study – Fixed times and the daily shiurim.