Have you ever tried to pair a seemingly basic necklace with an equally basic top and it still just looked ... off? Don't lie to me — I know you've done it because I do it all the time, and I write about fashion for a living. Contrary to popular belief, you cannot just slap any old piece of jewelry with any old top or dress.
The reason your necklaces aren't looking the way you want them to mostly has to do with their length, size, and overall shape, which are things we rarely account for when deciding what jewelry to wear with what outfit. The general neckline of your top is also an extremely important factor when deciding what jewelry to wear — or to buy, for that matter. When shopping for new bling, always take into account what kinds of shirts, sweaters, dresses, etc., you're most inclined to wear, and buy pieces based on that.
To get a better idea of which necklace/neckline pairing work best, watch this quick and simple video tutorial that'll having you picking jewelry like a Hollywood stylist.