Content is, of course, critical to creating a successful poster. Here are some key points to consider related to content.
Clearly state the purpose of your poster. If you don't clearly state what your purpose is, you probably don't know what it is. And if you don't know what your purpose is, you don't know what you are trying to communicate.
Your purpose also needs to be clear to your audience. If your audience doesn't know what you are trying to communicate, they will lose interest.
Your poster needs to be relevant to your intended audience, and the information in it needs to be relevant to your stated purpose.
The information should be significant, or of value to your intended audience. If the information is trivial or if it is common knowledge, it is probably not worth putting it into a poster.
Is all the information in the poster essential to your message?
Posters are not the same as research papers. Posters are intended to boil down a project or topic to its bare essentials, not provide details or supporting documentation. If some of your information is relevant but not essential to your main points, don't include it. Consider putting non-essential "nice to know" information in a supplementary handout.
Good organization is key to good communication. Good organization involves breaking down your content into logical categories. Organize your information into major sections. For example, a poster describing a quantitative study might include section headings such as:
Break down the major sections into subtopics or bulleted paragraphs.
Go to the Content example on the Design Elements: Examples page, evaluate a poster, and compare your evaluation with ours!