If entertainment magazines could only take one lesson from 2010, it should be: Put Lady Gaga on your cover. Gaga’s gun-strapping, bare-assed July Rolling Stone cover, seen at left, sold 245,000 copies by late September (these numbers come from the Audit Bureau of Circulations, who’ve so far only tracked sales through the fall). Gaga’s April Cosmopolitan cover sold 1.7 million copies, and her covers for Vanity Fair and Elle were also huge sellers in 2010.What other pop stars sold magazines this year?Rihanna’s January GQ and August Seventeen covers were both big sellers.And according to WWD.com, Taylor Swift had the year’s “poorest results.” Her covers for Elle, Marie Claire, and Glamour were among each of those magazines’ worst sellers of the year.What gives? That answer’s clear–Taylor’s wearing clothes.