Each time I see a girl walk by in a great dress or skirt I feel like pulling her leggings up about 5 inches.
They should ideally be worn just where the calf starts to narrow, not just above the ankle. Wearing it above the ankle, foreshortens the leg and instead of making the leg look longer, it makes a stunted shape.
The sexiness and the illusion of length disappear and leave you with a strange silhouette. The shoes look too near the end of the legging leaving a little gap of flesh at the ankle which looks puzzling and unattractive.
If you wear leggings make sure they are Capri length: no more than about 5 inches below the knee, this instantly disguises and slims down the leg.
If you are wearing a dress or skirt it works with the hem line. Have the tip of the legging just teasing its way past the end of the skirt - this can look so flattering, and conveniently keep the chill off this Autumn.