I found this video on YouTube, hope you learn something about judging cattle from it.
Beef is the easiest thing to judge for me. When judging cattle you want to look for muscle, volume, and structural correctness. When I come up to the class I first want to look at the animals from behind and place them in my mind according to how they look. Then I start working my way forward, looking at all the traits that make a good animal. After I have looked at the cattle (steer, heifer, bull) thoroughly, I find my top and bottom animals or the top and bottom pairs. After I found my easy pairs, I start to go into more advanced judging looking at less important traits or obvious structural flaws.
When you know the parts of the animal it's easier to do reasons and placings.