What makes a good poster?

To me a good poster has to have real good information that can capture the attention of not only one group, but can have the ability to capture other groups. Another thing don't just stay in one place, explore the whole page. You need to catch peoples attention, gloomy- plain looking picture is not going to do that. Even if it looks ridiculous, if you get them to even glance at it than you've done your job.