DO swipe three different color close together onto your jawline. The one that disappears into your skin is the winner.
DON’T test shades on your hands; they could be a completely different tone than your face’s.
DO know that the heavier the foundation, the more exact the shade needs to be; sheer makeup gives you more leeway.
When taking a selfie for one of the new skin-matching apps, DON’T do it inside, where your camera readjusts natural light.