When I first began to use LaTeX long ago, a friend of mine gave me a preamble and essentially told me to not touch it until I knew better. This was very helpful to me, and I immediately began to use LaTeX in a mindset that separated content from presentation. Later, I did know better, but I'd already gotten the gist of what's going on.
Years later, when I introduce LaTeX to others (which I have frequently done), I follow the same starting path.