struggling with light and shadows in acrylics

I’ve been painting with acrylics for a while, but light and shadows still feel really hard to understand. Sometimes my paintings look flat, even when I try to add darker and lighter areas.

I don’t really get where to place shadows or how strong they should be. And when I try to fix it, I feel like I just make things worse or muddy the colors.

I’ve watched some tutorials, but when I actually paint, I freeze and don’t know what to do.

How did you learn to see light and shadow better? Are there any simple exercises or tips that helped you improve?