Rule 7: Know a fad from a trend.                          

While you should invest in key trends, spend sparingly on passing fads - like harem pants and cobweb tights.

Rule 8: Acknowledge your age. 

With teens wearing vintage boxy jackets and Helen Mirren parading around in a bikini, the age line has never been fuzzier. But if you have to give it more than 60 seconds thought, that's a no.