A chain necklace is the one piece of jewellery that looks deliberate even when you've grabbed it off the dresser in the dark, and that's because the chain itself is doing the styling for you, no pendant required. I own four now, which is three more than I thought I needed, and the one I reach for most is the plainest, which tells you something about how little the rest of them were earning their keep.
It doesn't want company near the collarbone, so skip the layering with anything else that has weight or texture, a second chunky chain just reads as tangled rather than styled, save the stacking for the thin delicate ones if you want more than one at once. Gold tone is the easiest colour to live with because it sits against most skin without looking like it's trying, silver reads a little colder and sharper, which suits a plainer top but fights with anything warm toned or busy. Brushed or matte finishes forgive a lot, scratches don't show the way they do on high polish, and a slightly worn in look often suits a chunky chain better than mirror shine anyway. Where it comes unstuck is on anything with a high or fussy neckline, a polo neck, a ruffled collar, a shirt buttoned to the top, the chain has nowhere to sit and just looks stranded, and on very delicate, floaty fabrics a heavy chain can drag the neckline down in a way that looks accidental rather than intentional.
A chunky chain also has no business at a formal event where everything else is dressed up, it pulls the whole look towards the street rather than the room.
The difference between one that lasts and one that turns your collarbone green within a fortnight comes down to what's under the plating. A cheap base metal with a thin gold wash will wear through at the clasp and the links that touch your skin most, usually within weeks if you're wearing it daily, so look for stainless steel or solid brass underneath, they hold their colour and don't react with skin or perfume the way the bargain versions do. The clasp matters more than people think it should, a lobster clasp that springs shut properly beats a bendy spring ring that you'll fight with every morning and eventually lose the necklace to. Check how the links are joined too, soldered links sit flat and don't catch on jumpers, the cheaper open ones snag, stretch slightly with wear and eventually gape. A good one feels slightly heavier in the hand than you expect, that weight is mostly what you're paying for.
Buy one properly made chain before you buy three cheap ones, you'll wear the good one on the days you can't be bothered to think, which is most of them.