(photo from The Odd Twin, a simply wonderful vintage store in Park Slope)
I kind of chucked and said that more than half my clothes and certainly every interesting piece was made before 1980. She seemed stunned and followed up with one of my most favorite statements ever, "but they don't look old."
So, I told her my three secrets...
1. Fit: Fit is everything. If it doesn't fit you and it can't be tailored to fit you, you can't buy it. You wouldn't buy something new that didn't fit you so don't buy something old that won't fit you. It will make you look like you've been playing dress up in your grandmother's closet (side note: this might not be a bad thing if your grandmother was the same size as you.)
2. Shape: Shape is not to be confused with fit and could possibly be even more important. Never. Ever. Never buy anything that has a strange body-deforming shape. This means no shoulder pads and no blousey pleated pants. These things immediately date what you are wearing (and though they've come back in style they frankly should have no place in fashion.) The best shapes are simple ones; a-line dresses, fitted tops, pencil skirts and waisted jackets.
3. Pattern: A crazy pattern is like a bullseye. This is the mark of a careless thrift store shopper and better fodder for Halloween costumes than for your every day wardrobe. Pick simple patterns, big flowers (not little ones) and stripes are the best bet and the fewer colors the better. Unless you're going for the Laura Ashley look from the early 90's this will help make your look more contemporary.