1. Layer a button-less blazer over your fit-and-flare sundresses.
With the simple addition of a waist-length jacket, Rachel Bilson has turned her casual summer outfit into a legitimate early-fall look. This trick won't work with all blazers, though; the secret is to pick one that hits at the hip bone and doesn't have buttons. That provides just enough contrast without being too miss-matched.
You might get away with cutoffs like Alexa Chung here on the warmest of Indian summer days, but otherwise I suggest mixing this combo with distressed skinny jeans. Along with the army jacket, it'll stop your shirt from looking like a Coachella leftover (even if that's what it is).
While a sleeveless lace jumpsuit alone just screams mid-summer cocktail party, the way Diane Kruger's topped it with a leopard fur chubby has an It-Girl irreverence I love. I say it's a worthy (and party-ready!) look year round.
Between her shimmer-y top layer and metallic accessories, Olivia Palmero has managed to make these lightweight pastel shorts a lot more autumnal. The feminine sneakers help, too, since beat up Chucks would seem too summer vacation.