I see that I have stumbled across this thread rather late (the last post seems to have been in February!!). Nevertheless, I can't resist adding my penn'orth of wisdom as a woman who has lived (and is still living) all my adult life in France.
Don't under-estimate British chic. The French certainly don't! Magazines like Elle and Marie-Claire often devote pages to help their French readers achieve "le style britannique". Having said that, I endorse what other posters have said, it is impossible to be elegant without good grooming. Take care of your skin, hair, nails, and be prepared to make friends with your local cobbler and dry-cleaner. A good haircut, is, as others have said, essential. I have a plunging bob (short at the nape, but plunging at the front to chin-length). It's a cinch to maintain between my monthly visits to the hairdresser.
Contrary to some posters, I definitely believe in a capsular wardrobe and a careful choice of good accessories. Well chosen jewellery (gold or silver if possible, but worn discretely), even with the most casual of outfits. One simple outfit that has brought me countless compliments from French friends is a good pair of jeans, worn with a simple black scoop-necked T-shirt, a well-maintained black blazer, a Hermès silk square, and black patent pumps. Less is DEFINITELY more for the chic French look, but be prepared to buy the best skin products you can, use them conscientiously, then use natural make-up to let the results of your hard work show through. Finally, develop a signature perfume. For me, Guerlain have a great range of intemporal ones to choose from. I wear L'Heure Bleue, which dates to 1912!! How many other perfumes do you know that will stand the test of time like that, and still get you compliments? Good luck, but above all relax and enjoy developing your personal style!