Yeah...in the news today: Don't worry about these old fashion rules...
1. You Shouldn't Wear Black with Navy Blue. It's only true when it's a really DARK navy blue. If it's a LIGHT navy blue, wearing black with it is fine.
2. You Shouldn't Mix Two Different Patterns - its actually okay as long as one of them is more understated, so they don't clash too much. And they should also both have at least one or two colors in common.
3. If You're Overweight, You Should Hide It with Loose Clothing. The truth is, oversized clothes tend to make you look BIGGER, not smaller. And almost everyone looks best in clothing that actually fits.