You don't have to do the stereo-typical little black dress for a cocktail party. You can do a dressy pants suit or jump suit too. Long skirts, and tailored dresses in wools are great too. I think tailored jackets like a bolero design is a great way to minimize flaws if you choose a strappy dress. The more tailored the outfit, the more pulled together you'll look. Seems counter intuitive since tailored means it'll fit close, but it's the structure that helps with shape issues. Also invest in good undergarments that offer support and control. A body shaper is very helpful in redefining your figure if you're wearing thinner, flowy fabrics.
Raw silk, shantung (sp?), cashmere, and georgette fabrics are popular fabrics. And rich jewel tones and colors are appropriate in Fall and Winter. Rhinestone or jewel accents on your clothing such as a cashmere sweater, are fine as long as they're tastefully done. You can never go wrong with pearls. But always remember, less is more.