Search out fabulous evening wear and costume jewellery – pieces that never go out of style, says Lisa Armstrong

Top tip: Make a big fantasy wish list at the start of the season for any special pieces you fall in love with but can’t afford. It’s tempting to leave party dresses until the last minute because they’re not generally something you wear much and therefore a low priority. But that can lead to panic buying when you can least afford it – and succumbing to the cheap and not so cheerful. “Almost works” isn’t good enough. Classic evening wear details include heavy satins, floaty chiffon, sequins and beading – all of which cost a fortune when they’re done properly, but come with big reductions in the sales. Don’t be swayed by ephemeral details – exaggerated statement sleeves for instance are already on the turn. But a fabulous cocktail dress that fits and flatters will be a standby for years to come.

What she’ll be buying: This Diane von Furstenberg is a floaty classic that will look good at any evening events and it’s a great colour. Now that Jonathan Saunders is leaving the label, it’s also a style they may not repeat. These pearl earrings from Simone Rocha are a perfect example of simple-but-stunning – it’s almost crazy they’re on sale. Faux pearl earrings, £195 to £117, Simone Rocha (net-a-porter.com)

Silk gown, £540 to £378, Diane von Furstenberg (net-a-porter.com)