One thing I used to do was put my thumbs near the screen to cover up all but just the opening of two angles, and then compare them - but be careful not to touch the screen, you've got big brother watching.
Also, be sure to pick off the smallest and largest first. Also, if you're using Kaplan, be prepared to get questions that are much harder. I was getting like perfect on Kaplan and then the actual ones blew me away. Multiple times I said to myself "Aren't those all the same angle?" Haha