1. **State the problem:** Simplify the expression $9m^7 - 3m^2$. 2. **Identify common factors:** Both terms have a common factor of $3m^2$. 3. **Factor out the common factor:** $$9m^7 - 3m^2 = 3m^2(\cancel{3}m^{\cancel{7-2}} \times 3 - \cancel{1}) = 3m^2(3m^5 - 1)$$ 4. **Explain:** We factored out $3m^2$ because it is the greatest common factor of both terms. This simplifies the expression and makes it easier to work with. 5. **Final answer:** $$\boxed{3m^2(3m^5 - 1)}$$