In May of 2015 we had a great session with postdoc and frequent poster competition winner Dr. Ivan Liachko from the Dunham Lab about how to give a poster with lasting impact. The full notes from this incredibly useful session are here, and we are planning on running this workshop again in 2016 before the summer conference season.
A few quality external resources:
UW design help desk: http://depts.washington.edu/deshelp/
http://colinpurrington.com/wp-content/uploads/2011/09/scientific-poster-advice-purrington.pdf
http://guides.nyu.edu/posters https://nau.edu/Undergraduate-Research/Poster-Presentation-Tips/