With a one-shoulder gown you should avoid a long necklace as it would compete with the neckline of the dress. Focus on fun bangles and rings, and a shorter earring. Rose gold is really in right now and would play well with the periwinkle color. Avoid silver or you’ll get a “winter wonderland” look, which is dated and stale. Also, try to avoid skinny strappy sandals- they’re so played out and prom-ish… Maybe go for an open-toe platform heel in a fun, bright color. And if you need a bag, don’t get a typical boxy satin prom bag- look for something more unusual- like a lace hard clutch with a knuckle duster top, a Lucite clutch, or a vintage beaded bag.  Happy shopping!