The two terms of this polynomial have greatest common factor $3\text{,}$ so the first step in factoring should be to factor this out: $$3\left(x^3-1\right) \text{.}$$ Now we have two factors. There is nothing for us to do with $3\text{,}$ but we should ask if $\left(x^3-1\right)$ can factor further. And in fact, that is a difference of cubes. (Notice that $1^3=1\text{.}$) So we can apply Fact 7.5.15. The full process would be: $$\begin{aligned} 3x^3-3\amp=3\left(x^3-1\right)\\ \amp=3(x-1)(x^2+x+1) \end{aligned}$$