Footsteps.

Growing up, one of the sound effects I liked hearing in movies was the sound of footsteps. It's a very small detail of sound but for some reason it stood out to me, huh no pun intended.
Over the years it was the sound of footsteps that helped me open my ears to the other sounds in film.

Take this scene from Rian Johnson's movie "Brick" for example:

The footsteps in the beginning helps build up the tension to when he pulls out his knife.
Of course the first time I saw this I only heard the footsteps and the chase, I got the sense of urgency from each character by the sound of their footsteps as they ran.

I then started to notice the other sounds that came into play. The blood spurt when he cuts him, the echo their shoes made as they ran through the hall way, the crow and the dramatic DING in the end.

Honestly it took a few showings for me to "see" them but it all started with the sound and appreciation of footsteps.