Leaning visibly into the curve instead of staying nearly upright. Edge depth and flow are explicitly rewarded under the placement criterion — this is not a matter of taste.
Every blade has two edges, and you never really skate flat. A deep edge means leaning your body far enough into the curve that the blade cuts a clear arc into the ice instead of merely suggesting one. It feels like losing control at first — which is exactly why the typical mistake is staying flat out of nervousness. Flat edges look upright and tidy but cost flow, speed and points, because the placement criterion explicitly rewards edge depth and flow. The way there runs through repetition at low speed, not through courage: hold the curve cleanly first, then increase the lean. What often gets missed — edge depth depends on your equipment too. A blunt blade slides out sideways however convinced your lean is.