The thing nobody tells you about summer party dressing is that it is rarely warm enough for what the outfit actually needs, so you end up either freezing in a doorway queue or sweating through something structured by ten o'clock. I have stood outside more than one garden do clutching a cardigan I was too stubborn to wear because it didn't go. Still, this is the one stretch of the year where you can get away with colour, shine and a bit of skin without anyone blinking, and that is worth planning around properly rather than grabbing whatever's clean.
Colour wise, I have had the best run with things that sit between pale and bright rather than at either extreme. A soft coral, a washed out lilac, a proper true red, these all photograph well in evening light and don't fight with a tan or the lack of one. White is lovely until there's a buffet involved, and I say that as someone who ruined a white co-ord with a stray bit of salsa within forty minutes of arriving. Metallics earn their place too, but a soft gold or pewter wears easier through a whole night than silver, which can look costumey indoors under normal bulbs rather than fairy lights. What separates a good party piece from a sad one is mostly in the fabric and the finish. A dress that holds its shape without you tugging the hem down every five minutes, a slip skirt with enough weight that it doesn't cling in the wrong places, a sequin top where the sequins are sewn rather than glued so they survive a car journey and a dance floor. Zips that sit flat, linings that don't ride up, buttons that aren't already loose in the packet, these are the small things that tell you whether it'll make it through one summer or five.
Where it tends to go wrong is in the layering. A heavy structured blazer kills the lightness of a slip dress stone dead, and anything with its own print or sequins gets lost under a patterned coat, so keep the outer layer plain and thin if you need one at all. Chunky boots look wrong with anything delicate, and a bag that's too practical, the big structured work tote, will undo a floaty dress faster than a stain would. Plainer gold jewellery and a simple sandal let the outfit itself do the talking.
So before buying, I ask myself one thing: will I still want to be wearing this at midnight, not just at the start of the night?