My friends always comment that I have a great pair of eyes and that I glass so well. I think they are all becoming really good at glassing as well. The one thing that helped me and now them is, looking for parts instead of looking for the entire animal.
Numerous times I will see the shape of the letter "V" in a tree or bush while looking for Elk/Deer. I know from experience now that this is the top of the head between its ears.
I am constantly looking for colors. (Tan and White) which usually is going to be the rump of Elk (tan) or Deer (white). A few times the color white will also be a Mule Deer's face above his nose or under his neck
Look for objects that run parallel, the natural lay out of the forest or landscape is for everything to run vertical, if you train your mind to look for objects that are parallel, alot of times you are going to find what you are looking for.
This seems obvious, but on calm days looking for movement is one of my favorites, and I don't mean an animal running, but I am talking about the real small movements like tree tops moving or the flash of their tail's moving.
You will be making antlers grow on a lot of trees, shrubs etc, and see a lot of things that resemble a Deer or Elk. But its a lot like fishing, if you think there is something on the end of your line set the hook, if you're wrong you're wrong but its worth the effort, so the same goes for glassing if you think there is something there glass for ten minutes in that area to prove yourself wrong or right. It's worth the effort.