While I would hardly consider myself an expert at layering, I do have a few tricks that I know I can always rely on. A simple white fitted tee under a strapless dress, for example, or a collared shirt under a crew neck anything. But the one trick I rely on the most - and that seems to work more than any layering trick, is tying a button up around the waist.
While this style might have its roots in the grunge era, the effect can often be exactly the opposite. Especially when you're tying a button up around a beautifully crafted white shirt dress at your natural waist (as opposed to slinging the tied button up low around the hips) and even more especially when the button up and the dress are the same color.
I love the duality of the collars, and the fact that you are using the button up as more of a multi-dimensional, reconstructed belt than anything else, giving a previously loose silhouette an hourglass shape.
There's one more thing to note: opting for a crisp, white button up, or at times, a classically pinstriped pale blue button up, both more on the polished and preppy side, will give you an entirely different look from a typical plaid. Not that I don't dip in to my plaid shirt section as well for this trick, but the type of shirt used can make a major difference in the overall look.
Do you ever use this trick? What's your favorite way to layer?