There's a whole world of jewellery that's fallen out of fashion since around 1950: Dress clips. Dress clips had a heyday in the 1930s and 40s, but have been rather neglected since. They can come singly or in pairs, or sometimes in the form of a "Duette", where a pair can be fastened together to form a brooch.
How to wear dress clips
Dress clips can be worn in much the same ways as brooches, except that by their nature their primary use is to accent a neckline.
♥ Fasten a pair on either side of a sweetheart neckline.
♥ Clip into the pockets of a jacket, as worn by Ella Raines, 1947.
♥ Add interest at the point of a V neckline, as seen on Betty Grable, 1949.
♥ Clip at the collar of a shirt dress, as worn by Barbara Stanwyck.
♥ To accent the strap on an asymmetrical dress, as seen on Gene Tierney.
♥ Wear two on the same side of a V-neckline for a twist on the usual.
♥ Clip a pair into the top of a collared dress or blouse.
♥ Dangle from a velvet ribbon to make a statement necklace, a la Ann Miller.
♥ Use a single clip on one side of a V-neckline.
♥ Wear an oversize clip to add drama to a wrapover or surplice bodice.
♥ Clip a pair to the shoulder straps of a glamorous evening gown (source).
♥ Wear in the corners of a square neckline.
Vintage celebrity photos from Morning Glory Antiques.
Improvise dress clips
If you're still looking for the perfect pair of Art Deco dress clips but want to try the look, vintage clip-on earrings can do double duty as dress clips.
Sparkly hairclips would also work just as well. You could even make your own by attaching beads, buttons or a lightweight broken brooch to a clip back (you can get clip-on earring backs on ebay or etsy).