Lines: The eye naturally follows lines and all clothing has lines. The lines in clothing are necklines, pockets, sleeves, hems, etc. For example, a sweater that has v-neckline will draw the eye downward creating a long line, the look of a longer neck, longer face and slimmer upper body. By contrast a turtleneck creates a short, horizontal line that stops eye and makes the face appear fuller, the upper body bigger and the neck shorter. Using this concept alone you can create a slimmer upper body by sticking to tops with vertical lines that create the look of length; and by stashing the turtlenecks until you feel a little slimmer.
Color: Keep in mind that black lessen and white increases. This is important in wearing designer clothes because it means that darker colors will make the wearer appear smaller and lighter clothing will make the wearer look larger. Wearing black to look slimmer is a trick that has sometimes been commonly used. Black does have a slimming effect but too much black can be lifeless and create a washed out look if the proper makeup is not worn. Some women who want to look smaller try the smaller size. Remember that tight clothing will always make you look larger. It is much more emphasizing to wear clothing that fits well and glides over the body rather that sticking to it. Wear dark colors on the places you want to appear smaller but be sure not to wear them tight. For example, if you are a triangle shape with a larger lower body than upper body and you want your lower body to appear smaller, wear a light color top with dark pants or skirt. For an overall taller and slimmer look, dress in the same color from head to toe.
Proportion and Scale: An object seen next to other objects appears either larger or smaller depending on the size of the objects that appear next to them. For example, the size of a handbag in relation to the woman carrying it. A large woman carrying a small handbag will appear larger. To avoid looking larger when wearing prints, keep them in proportion to your size.