I love to wear brooches pinned on straps of little summer tanks. Totally ups the glam factor and eliminates the need to wear a necklaces... necklaces just get in the way during the hot summer weather.
I also like to wear pins near the waistband of ruffled skirts and on the label of my denim jacket - and if a tee is a little too big, I use a big brooch to gather it together at the hip.
Edited to add that often instead of buttoning up my cardigans, I just fasten with a sparkly pin - stole that idea from a TeenVogue a few months back.