The Rebbe's letters on the finances of shuls, schools, yeshivos and communal organizations, in two parts:
Money troubles in shuls, schools and organizations — Communal money as a trust, not letting a deficit pile up, relying on your own fundraising, keeping going through hard times, and reporting promptly.
Fundraising for shuls, schools and institutions — The mission before the money, fundraising trips abroad, coordinating campaigns, what works, planning prudently, and treating donors properly.
In short: The Rebbe treated communal money as a sacred trust and asked those responsible to manage it carefully, plan ahead, and keep donors' trust through transparency and timely action. At the same time he insisted that money is a means, not the goal: an institution's spiritual work must never be cut back or pushed aside for fundraising, and every fundraising effort should itself spread Torah and Yiddishkeit. Difficulties are expected in holy work; what decides the outcome is the determination of the people running it, unity among them, and trust in G-d.
For personal and family money matters, see: Livelihood (פרנסה).