Layering necklaces: a simple three-chain formula
Start with a short chain that sits at the collarbone, then add one that falls about two inches lower, and finish with a longer pendant. Staggered lengths keep the pieces from tangling and let each one be seen.
Keep one piece as the focus. If the longest chain carries a pendant, let the other two be plain. Three busy chains compete; one hero and two supporting pieces look deliberate.
Stay in one metal tone for an easy look. Mixing yellow and rose gold works too, as long as one of the pieces already combines both so the eye reads it as a plan.