Page 1: Introduction
New designers tend to put text and graphics on the page wherever there happens to be space, often without regard to any other items on the page. What this creates is the slightly-messy-kitchen effect-you know, with a cup here, a plate there, a napkin on the counter, a pot in the sink, a spill on the floor. It doesn't take much to clean up the slightly messy kitchen, just as it doesn't take much to clean up a slighty messy design that has weak alignments.
Robin's Principle of Alignment states, "Nothing should be placed on the page arbitrarily. Every item should have a visual connection with something else on the page." The principle of alignment forces you to be conscious-no longer can you just throw things on the page and see where they stick.
When items are aligned on the page, the result is a stronger cohesive unit. Even when aligned elements are physically separated from each other, there is an invisible line that connects them, both in your eye and in your mind. Although you might have separated certain elements to indicate their relationships (using the principle of proximity), the principle of alignment is what tells the reader that even though these items are not close, they belong to the same piece. The following pages illustrate this idea.
Source: The Non-Designer's Design Book by Robin Williams