How do I break a long equation over lines?

I am trying to add an equation in a new line. The problem is that the equation is too long for the line, and I need to break it manually. Otherwise, it just overlaps to the right column, or to the right margins (and looks ugly...). Is there a way LaTeX can brake the equation for me, so it seems nice?

I'm attaching my latex code:

\begin{align*}
f(n)-f(0) &= A(n)-B(n)-C(n)-D(n)\cdot d-\left(A(0)-B(0)-C(0)-D(0)\cdot d\right) \\
          &= A(n)-0-X-D(n)\cdot d-\left(0-0-0-0\right) \\
          &= A(n)-X-D(n)\cdot d
\end{align*}

The problematic line is the first line, which is too long.