I think the problem with many women in, let's say, UK/US, is the desire to always wear the very latest fashion as not to look 'dated'.
Most high fashion/trends derived from it, unfortunately, doesn't suit the majority of women, well, unless they are size zero and 6ft tall.
Not a popular view on MN, but Parisiennes, some of them, clearly not all, are sex-appeal, style and casual carelessness personified, yet often wear couture pieces that belonged to their grandmothers.
Talk about 'dated' if one wanted to be literal.
My recipe would be to find the style that suits you, your body and lifestyle, and then get the best quality basics, as from proper fashion houses, not high-end high street (eBay is the best as otherwise prohibitively expensive for most).
Buy a couple of fun 'current' bits every year, high-street stuff for 'trends' and you'll have the wardrobe that flatters forever.
As for sexy, again, go with what suits you, appropriate for the occasion, never overdone.
To me, an instant style-remover and in some ways, a class-identifier, is the hair straightening craze, (sorry to drag the class into it) just so awful, why do people do it? No-one looks good with ironed hair.
Same for salon blow-dries, so American 'cheerleadery'... 
Another unpopular opinion of mine concerns the bloody trainers. Unless one is a blossoming teenager, trainers do not, categorically, look remotely sexy. Sporty, boho - yes. Sexy - never.