You can spot a good white ring from the other side of a room because it still looks clean at the end of the day. A poor one goes dull within a week, the plating thinning at the edge where it meets your finger, the white turning a faint yellow that no amount of polishing cloth will fix. One sits bright against the skin for years. The other starts apologising for itself almost immediately.
If you have none at all, start with a plain band rather than anything with a stone or a pattern. A simple white band in a decent metal does more work than you'd expect, it sits against almost any other ring you add later, and it gives you something to judge future buys against. Once you know how a good plain one feels and wears, you'll spot a weak one in a shop in about three seconds. What actually separates the well made from the disappointing comes down to a few boring but important things: solid metal rather than a thin plated layer over base metal, a band with enough weight that it doesn't feel like foil, and edges that have been finished smooth rather than left slightly sharp where they'll catch on jumpers and tights. Hardware matters too if there's any kind of fastening or adjustable element, it should move without catching and not loosen on its own after a few weeks of wear. Cheap ones often look identical to good ones on the first day, the difference only shows up after washing hands fifteen times a day for a month.
In the shop, run your finger round the inside of the band before you buy anything. Any roughness there will rub, and you will feel it by the end of a long day, usually right at the point it crosses the knuckle. Check the join if there is one, a soldered seam should be invisible, not a visible ridge you can catch a nail on. Hold it up to a window rather than the shop's warm lighting, which flatters every metal equally and tells you nothing true about the actual colour. And try it on cold hands as well as warm ones, rings that fit perfectly after a hot commute can feel tight an hour later when your hands have cooled down, which tells you something about sizing you won't get from a mirror.
For everyday wear, a white ring sits easily next to gold without looking like a mistake, which surprised me the first time I tried it, I'd always kept my metals separate out of some rule I'd never actually questioned. It also pairs well with a plain watch, a simple chain, denim, knitwear, anything that isn't fighting for attention. It is, in the end, the ring that survives being thrown in a bag on the way out the door, which is most days for most of us.