This summary is drawn from the Rebbe's letters to him (about 5717–5723, 1957–1963); I did not find a published biography.
Spreading Chassidus despite opposition. The Rebbe urged expanding outreach with dedication and clarity about Chabad's unique approach (IK 4593), and wrote that opposition to spreading the wellsprings should only inspire redoubled effort (IK 5127). Influencing others requires sensitivity to each person's character (IK 5330).
Torah and institutions. Perseverance in Torah study and communal involvement brings Divine help (IK 8118), and expanding Torah institutions requires unity among their leaders (IK 8194). On educational materials, he advised using whatever design best engages the students (IK 8748).
Sources: the Rebbe's letters cited above.