Here's how:

Choose darker colors as the basis of your wardrobe, such as navy, black, charcoal grey, olive green, chocolate brown.
Use undergarment foundations, from all-in-one shapes to control-top pantyhose.
Focus on playing up your best features - for example, showing off shapely legs with a knee-length skirt.
Choose fabrics that don't cling, whilst avoiding stiff or bulky textures.
Use accessories to draw attention to your face, such as scarves, earrings, etc.
Avoid anything too tight or clingy.
Make sure you scale your accessories - from your handbag to your earrings - to suit your size.
Add small subtle shoulder pads to sweaters and other knit tops to make them hang better.
Design clean-lined clothing without big embellishment or buttons.

Prints should be scaled to your body - for example, no large prints if you are a fuller figure. In general, it's the space between prints that makes them unflattering, so look for prints that have overlapping images.
Don't shy away from sleeveless garments, especially with evening wear when you can cover up with a shawl, sheer top or a jacket instead.
Don't think that baggy clothes make you look slimmer. Body-conscious clothes that hint at your curves - without being clingy or tight - are the most flattering.