developing a clinical eye

Hi! I'm a new grad nurse. After a 3 month orientation/training, I've been on my own for 2 months now and I just want to ask the older/more experienced nurses in this forum on how to develop one's assessment skills / clinical eye. For example, I had a pt who had difficulty breathing and my manager pointed out to me "don't u see that he's already using his accessory muscles?". This may sound dumb but honestly, I didn't notice that because I just thought it was just part of him being skinny. Plus, the CNA told me that his O2 sat was above 95%.

Then, there was another pt who was foaming in the mouth. I just thought that it was just saliva. Like, some people who fall asleep and saliva pools at the side of their mouth.

I know I sound really stupid but I am eager to learn. Would appreciate any helpful tips.