The boning is what separates a good corset dress from a bad one, and you can usually tell by picking it up before you even try it on. If it's flexible plastic stitched into thin channels, it will roll and dig by the end of an evening. If it's got proper structure, flat steel or firm moulded panels that hold their shape when you bend the dress in half, it will actually do the job a corset is meant to do, which is hold you rather than just decorate you. On me, with a longer torso than most, cheap boning gives up around the ribs and the dress just becomes a normal dress with seams. The good ones keep working all the way down.
A corset dress pairs better with plain things than with anything else that's trying hard. A flat sandal or a simple court shoe, a clutch rather than a bag with buckles and straps, hair left alone rather than styled to match. The dress is already doing the talking through the shape of it, so everything else should go quiet. I've made the mistake of adding a statement earring and a bold lip and ending up looking like I was trying to win an argument. Let the structure be the only loud thing in the outfit.
Colour matters more here than in most dresses because the eye is already drawn to the shape, so a busy print fights the boning for attention. Black, bottle green, a deep wine, these read as considered rather than as fancy dress. Satin finishes photograph beautifully but crease if you sit down for longer than a bus journey, so if you want one dress that survives a whole evening rather than just the first hour of it, go for a matte stretch fabric with the structure built in rather than bolted on.
If you've none of these and want to start with one, go for a knee length version in a plain dark colour with visible but not exaggerated boning, nothing with a dramatic lace up back unless you enjoy asking someone else to do it up for you. It's the shape that does the work, not the embellishment, and a simpler cut will get worn far more often than the one with the corset front and the full skirt that only suits one kind of night.
The mistake to avoid is buying it a size up because the boning looks tight in the mirror. Corset dresses are built to be snug through the body by design, and a size up just means the structure sits in the wrong place and does nothing at all.