Some horizontals -- especially those low on your body -- can sneak up and saboutage your look. 

Hemlines form unexpected horizontal lines, and the fuller the skirt or pant leg, the more horizontal the effect.  Keeping garments narrower and color-toning hosiery to the garment can minimize the shortening effect.

Henlines that end at an awkward spot on your leg are especially challenging. 

For skirts, just above your knee is attractive if you are young and slim.  More mature gals or those of us with a few extra pounds look better with a hemline that casts its shadow just below the knee.  The fuller area of the calf is "no man's land" for hemlines, but the pont where the calf narrows again is typically a flattering length.

Skirts should always be hemmed to create a longer-than-wide visual.  Otherwise the entire garment becomes a horizontal profile - yikes!

For pants, longer is better for typical leg styles.  Ideally the hem should fall about 3/4" from the floor in back and break just slightly over the shoe in front. Too-short "flood pants" anchor sideways emphasis at or above your ankles -- anything but sleek looking.

A skinny pant leg obviously can't fit down over the foot that way, but its narrow profile avoids that hemline horizontal problem anyway.

In the same realm, a jacket or over-shirt hemline needs to hit at a flattering spot on your body.  For example, by trying to bring a jacket down far enough to cover wider hips you could end up making your legs look shorter and your entire body look heavier.  Try a shorter  length instead, and minimize the vertical emphasis by choosing curved or elongated hemline shapes.

If you pair tall boots with a skirt, avoid the potential horizontal "gaposis" by wearing coordinating tights. 

And regardless of seasonal shoe trends, be very careful about shoes with ankle straps or other detailing that visually shortens your legs. 

Horizontal details at your wrist can also be distracting, since they fall right at the hipline when your arms are at your sides.  Think twice about decorative or flip-back cuffs and chunky bangle bracelets. 

How can you improve favorite outfits by minimizing distracting horizontal effects?