White space is, naturally, the part of your poster that doesn't have any words or images on it. White space is an important element in poster design, because it:
It might be tempting to fill up all of this space with text and images, but that makes it hard for someone to read through it. Here's an example with very little white space:
As you can imagine, this would be a tough poster to read through. Be sure to preserve as much white space as you can when designing your poster. Oh, and white space doesn't have to be white.
Flow refers to how easy or difficult it is for someone to read through your poster. You can improve the flow of your poster, and help people read through it faster, but using the following design elements:
Organize by Columns
Many people are used to reading from left to right and from top to bottom. Organizing your information into columns takes advantage of this fact and aids in comprehension. Otherwise, people can get lost trying to follow the information you are presenting.
Use "Visual Grammar"
People are used to following certain design rules without thinking about them. Most people, for example, recognize that section titles in an article are usually a little larger than the rest of the text and may be a different color or in bold. You can use these same rules to help guide people through your poster.
Include Organizational Clues
You can include numbers, letters, or arrows to guide people through your poster. For example, you could number each section to indicate the order that people should follow.
This example illustrates how all three of these rules can be used in your poster:
There are two things to consider when talking about alignment:
First, there should be a good visual balance of text and images. You can achieve balance by arranging the elements on your poster and using white space so that they roughly reflect each other horizontally and vertically:
Second, make sure that the individual sections of your poster are aligned with each other. You should avoid situations where elements are arranged in a haphazard manner like this: