Gold plated necklaces have a reputation for being the thing you buy when you can't afford the thing you actually want, and for a while that's exactly how I treated them, a stopgap until I could stretch to solid gold. I've come round. A good one looks every bit as rich as the real thing from across a room, and across a room is where most people are looking.
The difference between one that lasts and one that turns your collarbone green by March lives in the plating thickness and what's underneath it, though you'll rarely see that written on the label, so you're judging by feel instead. Pick it up and the clasp should feel solid, not like it'll bend the first time you fumble it on in a dark hallway. The chain should sit with a bit of weight, not float, because the cheap hollow ones catch on jumpers and snap within a month. Look at the join where the pendant meets the chain too, that's where the plating wears thin first and where you'll first see the dull brass or silver underneath creeping through. A fitting that's slightly brushed rather than mirror bright tends to hide that fade for longer, which matters more than it sounds like it should.
Where it earns its spot is in how little it asks of the rest of you. It sits well against bare skin in summer, under a collar in autumn, and layered under a jumper in winter where only the pendant shows at the neckline, which I think is the most flattering way to wear any necklace, honestly. It pairs easily with denim and a plain top on an ordinary Tuesday, and just as easily with the kind of dress that needs one good thing near the face rather than three competing ones. Warmer weather suits it best skin on skin, no fabric rubbing the plating off before its time, and that's also when scratches show least, since everything's a bit more relaxed and less likely to get caught on a scarf or a seatbelt.
For occasions, it's the piece that goes to a christening, a Sunday lunch, a work drinks and a wedding without anyone clocking it's done the rounds, which is the whole point of a good gold plated piece rather than a flaw in it. If you're starting with nothing in this category, go for a simple pendant on a fine chain over anything chunky or stone set, since the plain shapes wear the longest before you notice any fading and suit the most necklines.
Start with a warm yellow gold rather than a rose or white toned plating, it photographs better, ages more gracefully, and goes with almost everything else gold you already own.