Cocktail party dressing sits in a genuinely interesting middle ground. Not as formal as black tie but considerably more dressed up than your average night out. It is the occasion that rewards you for actually trying rather than just reaching for the reliable going out dress you have worn seventeen times already. Knee length to midi is the sweet spot. Something with a bit of personality. Fabric that looks intentional rather than just inexpensive. The cocktail party is one of the few occasions where being slightly overdressed is genuinely preferable to being underdressed and that should be liberating rather than stressful.