Hi Am new today and have just picked up on this thread. I actually work as an image consulant and some of these threads are proving interesting!
What you choose will be affected by the size of your boobs basically. If you are heavy busted then a longish necklace will only dangle off the edge and add too much interest to the 'busy' area. But don't go too tight round the neck either. Also, if the dress has a print then you need to keep the necklace to one colour otherwise it will get lost. If you are small on top i agree with amIwhatandwhy - you need to keep it busy on top and really need something on the neck area but long to the bust in layers will work well.Hope this helps