Make an outline of your poster on a normal sheet of writing paper. This will help you work out the details before you permanently make changes to the poster.
Place the title of your poster near the top of the poster. Consider that readers and listeners will want to know right away what they're in for.
Design the poster so that the information flows from left to right, top to bottom. This makes for easy reading and comprehending. Others will have a difficult time following along with your presentation if they cannot connect one idea to the next.
Keep any written text brief and legible. If possible, type it up, print it out, and then place it on the poster. As a rule of thumb, use bullet points instead of paragraphs. The point is to convey the main concepts without detailing what they mean. Any explanations, definitions, and details should be covered in your speaking points during the presentation.
Use the outline you've created as a guide for creating the final poster. Remember to keep your audience in mind. If you'll be presenting to children, for example, consider using eye-catching photos and colorful visuals as a means of grabbing their attention. In a business setting, keep the visuals more formal.
Proofread the poster the same way you'd proofread a speech or paper. Since the poster will be guiding you and others through a presentation, make sure it is accurate and well-edited.