This NYU guide is easy to understand and can help you fashion and frame the information you need to get out to your patrons.

Screen shots from article demonstrate in an instant the difference between 2 densely designed information boards showing 'effective easy to understand' and 'messy confusing' layouts.

http://guides.nyu.edu/posters

Also visit the Cooper Hewitt on line piece showing their exhibition demonstrating very clearly how poster ‎designers use visual keys to catch our eyes and minds.

http://www.copperhewitt.org/events/current-exhibitions/how-posters-work

Screen shots of posters: Cooper Hewitt