I always quickly meet the gaze, and give a confident girl-smile, then look away. That's the typical female "Identification of Friend or Foe" interaction.
If you're at all nervous or self-conscious or afraid of being read, GG's will pick up on that in an instant, and then the microscope comes out and it's all over.
On the other hand, if you're genuinely relaxed and confident, she will most likely smile back and move on.
If you don't move well (and in my experience many CD's don't have it down), that will get you read in a hurry, too. If you're tall or big, any deviation from the norm (such as a non-feminine gait) is even more attention-grabbing.
Women notice details much more than men (when they're in noticing mode and not preoccupied with what they're doing).
When a woman looks me up and down focusing on my legs I know she's admiring them, not reading me
