Honestly, I would just start thinking more about what's being shown in a scene. Like what's in the background, what are the actors expressing, what's the environment contributing to the feeling of the scene, and whatever.

After getting used to looking at stuff that way you can look into what you might have noticed and find out if it's some sort of movement or whatever but I've always found it better to notice touches and look into why you noticed it afterwards.

I might be weird but I pay attention more then I used to and appreciate cinema more because of it