There are some very good video’s on YouTube to help you understand Dog Body language.
www.youtube.com/watch?v-8bg_gGguwzg Understanding Dog Body Language – Learn how to read Dogs Behavior by: Krissy Kris
www.petprofessionalguild.com/Dogbodylanguage This is also good it has written descriptions and a short video.
www.pawsacrossamerica.com Has pictures and descriptions of dog cues.
www.moderndogmagazine.com Also has Pictures of dog cues.