This simple chart by Jessica Hagy is perfect when you think about web pages:

A single web page addresses a single topic. As the amount of information on your site grows, each page’s ability to walk this fine line grows more important.

Include the right amount of information—no more—and give the visitor a clear set of next steps. (You may have heard of these next steps referred to as “calls to action.”)

Even as a writer, you are also a designer.