Dress codes are shorthand, and the shorthand has drifted. Black tie now means floor length or a very formal midi, in a fabric with weight: crepe, satin, velvet, heavy silk. Cocktail means midi or knee length, and it is the most forgiving code, which is why most guests over-formalise it. Garden party and daytime mean colour, lighter fabric and a hem that can survive grass. If the invitation says nothing at all, the venue tells you: a hotel ballroom at seven asks for something closer to black tie, a vineyard at two does not. Two rules hold across every code. No white, ivory or anything that photographs as either. And nothing that competes with the wedding party, which in practice means no full sequin gown at a small daytime ceremony. When you are genuinely unsure, err one notch more formal than you think and remove a layer rather than adding one.

Look at the fabric before the shape. Crepe holds its line through a long day and does not crease on a chair; linen looks beautiful for an hour and then looks slept in. Satin shows every ripple, so it wants a smooth line underneath. Chiffon moves well outdoors but is see-through in bright sun, which is a real problem for an afternoon ceremony. Then the hem. Floor length needs the heel you will actually wear, so hem the dress to those shoes and not to a pair you are hoping to break in. On grass, a heel needs a wide base or you will spend the reception on your toes. Check that you can sit, reach for a glass and raise your arms without adjusting, because you will do all three constantly. If a dress needs a specific bra you do not own, buy the bra at the same time or the dress will never leave the wardrobe.

The dress you wear again is the one that is not obviously a wedding dress. A dark midi in a good fabric goes to a wedding, a work dinner and a birthday; the pale embroidered gown goes to exactly one wedding. If you want the memorable option, put the drama in the shape rather than the print, since a strong silhouette in a plain colour dates far more slowly. Build the outfit so accessories carry the occasion: one pair of earrings, a small bag, a shoe that can walk on the surface at that venue. Bring a wrap if the ceremony is outdoors and ends after sunset, because every outdoor wedding gets colder than anyone plans for. Steam rather than iron, and hang the dress the night before.

Most guests are dressed slightly wrong in the same direction: too formal for the daytime and too casual for the ballroom. Read the time on the invitation before you read the code. Do not buy a strapless gown unless you have worn one for six hours before, and do not buy anything that needs a stylist to sit down in. Skip the trend colour of the season, because these photographs stay in circulation for decades. If you take one thing away: choose the fabric first and the shape second, because a good fabric in a simple cut will look composed at eleven at night, and a bad one will not survive the receiving line.