What are the steps for factorizing $1 - ab - cd + abcd$? I can see that $1 - ab - cd + abcd$ factors to $(1-cd)(1-ab)$ but only because I tried a lot of different factors in a trial and error method, so it took me a while. I was wondering what the pattern to observe is and what the general/efficient method for factoring something like this is?

The steps are usually called "factoring by grouping."  As all factoring is basically educated trial-and-error, you should be encouraged that you found the correct factorization.  Anyway, here's more detail about factoring by grouping:
$$
\begin{align*}
  1 - ab - cd + abcd &= (1-ab) - (cd - abcd) \\
  &= (1-ab) - cd(1 - ab) \\
  &= (1-ab)(1-cd).
\end{align*}
$$
The crucial steps are: finding groups that look very similar -- with a goal of factoring a gcd from each group.  If each group now contains the same expression in parentheses, then that expression can be factored out.
Hope this helps!
