Layering is the one fashion skill I never seem to execute properly. 
It appears as if great complexity and creativeness is exerted into each 
ensemble; however, with these tips, layering just got a whole lot 
simpler.
CROPPED & LONG 
(For me, this layering technique was always difficult because somehow
 I always looked like a bloated clown) With this look, the most 
important component is the dramatic distinction of the layers; in other 
words, the cropped piece ends way before the hem of the second layer. To
 add a little spunk, combine solid colors with classic patterns.

(Sweater over Shirt)
By Kelly L.
VEST & JACKET
Accentuate the waistline by wearing a belt or a top that grazes the 
middle. The key concept to this look is to invoke a sense of balance; 
thus, a lean and fitted item for the bottom portion will neutralize the 
bulkier top pieces. It is best to choose a light, loose, and seamless 
jacket.

(Vest over jacket)
By Danielle R
LONG SLEEVE & SHORT SLEEVE
Atypical casual layering technique using a T-shirt but boost it up a 
notch (and have fun) by using other pieces such as sweaters, dresses, 
and blouses. Again, the second layer needs to be lean and fitted so that
 the look does not appear bulky.

By Saray D.
(Sweater over dress)
LONG & LONG
The primary layer needs to be slim-fitted and rest below the butt. 
Ensemble then appears as an elongated, slim silhouette. It is important 
to work with one light, flowy material because with this technique, the 
usage of too much heavy pieces may appear corpulent. Best to wear heels 
or platforms.

(Sweater coat over dress)
By Kasia G.
Happy Layering!
Hugs and Kisses
Audrey
Source: Instyle Magazine September 2011, Lookbook.nu