This should be A1 (59.4 × 84.1 cms, 23.4 × 33.1 inches) or larger, laminated if possible and clearly laid out. You are encouraged to use pictures/photos/diagrams to clarify and illuminate particular points. Some examples of posters and design ideas can be found by using the link below:

Design of Scientific Posters

Many people like to take away some additional information, so you might find it helpful to prepare a hand-out. Since they will already have an abstract relating to your poster, it should either be rather longer or give additional information or both.