This is one of my favorite things to show in my quilting class:
I wish I could hear your appreciative murmurs and "oh"s right now like I hear in class. These two blocks above were pieced exactly the same. See that? Pink in the middle, orange on the edges. But then I quilted them differently and they don't look the same anymore do they? The one on the left feels like it has more pink than the one on the right. And the one on the right has more orange now that it's quilted. Isn't that strange? This is how I teach the lesson: what you don't quilt is as important as what you do: anything you don't quilt lifts up and comes forward on the quilt and catches the eye.
Here's another thing I like to show; two swatches quilted very similarly. But do you have a favorite?
I sure do! The one on the left is so powerful, that center ribbon comes forward because the horizontal lines are quilted more densely. They smash down and become the background, allowing the wavy line to poof up and catch the light. In the swatch on the right the spacing between the straight horizontal lines and the vertical wavy lines is so similar, there is no foreground or background created so the piece ends up looking flat. What I want you to notice is I didn't do anything hard here: wavy lines and straight(ish) lines. I just made a choice with how to use those lines to play with the light and shadow effect of quilting. You can do this too!
Here's a sample from my Craftsy class Wild Quilting where I talk about this concept a fair amount. Just quilting densely around any motif pops it forward and creates a "wow" effect. When there's a big difference in density like above (look at the largest open space in the spiral design as opposed to the largest open space in the flowers and leaves) then you get a lot of drama. But it doesn't have to be dramatic. In the swatch below there's less difference in density. The open space in the feather and the wavy lines are not as far off. There is still a foreground/background created, but this one has a subtler effect.
I hope this gets your quilting wheels turning! More hot tips coming soon (ish).