Starlets gunning to make the Oscars' best-dressed list this weekend should take notice. We've been studying the most sartorially savvy leading ladies over the past 10 years and have noticed some key trends to heed for those wanting to join the elite ranks of the best dressed.

Rule No. 1: When in doubt, go with a European designer. (Sorry, CFDA!)

Eight out of our 10 favorite Oscar dresses of the past decade have come from designers who show in either Paris and Milan: Valentino (Julia Roberts, 2001; J.Lo, 2003), Elie Saab (Halle Berry, 2003), Gucci (Charlize Theron, 2004), Guy Laroche (Hilary Swank, 2005), Versace (Penélope Cruz, 2007), John Galliano (Freida Pinto, 2009) and Givenchy (Zoe Saldana, 2010). Michelle Williams (Vera Wang, 2006) and Amy Adams (Proenza Schouler, 2008) defied these odds, however, and won big with American talent.

Rule No. 2: Opt for a dress that's had little to no exposure.

One can ensure this by going completely custom, of course, as was the case with Williams, Adams, Cruz and Theron. Another popular approach is to select a gown from the most recent
couture collection (Saldana) or spring-summer offerings (Swank, Pinto), many of which have yet to arrive in stores by the time the Oscars roll around.

Rule No. 3: Look to the past à la Lopez and Roberts, both of whom chose frocks from the storied Valentino archives for classic yet fresh gowns.

Lopez's one-shouldered mint floor-duster had been worn only by Jackie Kennedy, 35 years prior, while Roberts' graphic black-and-white number from 1992 is often pointed to as the dress that helped popularize vintage on the red carpet.

Rule No. 4: Rules are meant to be broken! And we absolutely can't wait to see what this year's ladies have up their sleeves.

In related news: Check out our red-carpet style prediction for Sunday night's nominees.