Spot the difference from across a room, every time. A good red dress has one true colour running through the whole thing, a red that looks the same under office lighting as it does walking past a window, while a poor one goes orange under the wrong bulb or looks like it's faded before you've even washed it. The good one holds its shape when you move. The poor one looks like a costume the second you sit down.
Keep it away from anything that's trying just as hard. Busy prints, metallic shoes, a bag with its own opinion, all of it fights for attention the dress already has, and you end up looking dressed by committee rather than by yourself. The easiest pairing is the plainest one you own, a black cardigan, a denim jacket, plain nude or black heels, a flat white trainer if it's daytime. Let the dress be the loud one.
It's not the right choice for everything, and I'd rather say that than pretend otherwise. If you're self conscious about being looked at, a bright red dress will get you looked at, that's just how it works. It's also not forgiving on a day you feel bloated or tired, because the colour draws the eye exactly where a softer shade would let you hide a bit. There's no shame in reaching for navy or bottle green on those days instead.
What separates the ones worth having from the ones that end up at the back of the rail usually comes down to the fabric doing something other than just existing. A dress with a bit of weight to the skirt will swing and settle properly, a thin, slippery fabric clings in the wrong places and creases if you so much as lean on a table. Check the lining too, a cheap one goes see through under certain lights and you won't know until you're stood under one. Zips should sit flat, seams should lie without puckering, and if there's a tie or a belt it should actually match the dress rather than being a slightly different, sadder red tacked on as an afterthought.
On shade, a true red, the sort that leans neither orange nor pink, is the easiest to wear against most skin tones and the easiest to repeat without it looking like you're stuck in a rut. A deep, almost wine red is kinder for daytime and office wear if bright red feels like a lot. Bright, clear red is lovely but it's the one that shows every mark, every crease, every bit of sun cream you forgot to blot off.
A red dress that's cut well does more for how you stand than any amount of fussing with accessories afterwards.