The Rebbe's guidance on trust in Hashem and worry about making a living:
Parnassah comes from Hashem; our effort is only the vessel. Natural effort is necessary, but it is a channel for Hashem's blessing, not the source of it. One needs to act only as much as a vessel requires, and overexertion can actually hinder success (IK 825, 4274, 7304). Trust in Hashem itself brings the blessing more quickly (IK 5450, 5544).
Don't live in anxiety over money. Don't worry over short-term ups and downs in business; periodic accounting is enough (IK 2516). Don't rush into financial decisions out of fear of loss (IK 5644). Where possible, seek a livelihood that allows peace of mind, and move toward it gradually (IK 7158). Developing more than one skill helps (IK 3275).
Hardship is a test, and it is temporary. Financial struggles are tests meant to strengthen trust, and they pass (IK 2461, 7267, 8058). After a loss, don't despair; a setback in one place often opens a new path elsewhere, and recalling past times one got through similar difficulties gives strength (IK 4279, 5805, 7140).
Never compromise Torah for gain. A livelihood from Hashem does not require compromising Torah and mitzvos, and financial struggles are not caused by observance (IK 2119, 3303, 6013).
Keep your joy. Temporary financial stress should not overshadow joy and gratitude for one's blessings; joy breaks through barriers (IK 1618, 3558, 8739).
Practical and spiritual steps: seek advice from trusted friends, increase tzedakah (especially daily), say Tehillim, and strengthen bitachon by learning Psalm 23 and the Shaar HaBitachon of Chovos HaLevavos (IK 6437, 7103, 8757, 9992, 10787). Make the business itself a means of serving Hashem (IK 1105, 4602).
See also: פרנסה – צדקה ומעשר.