1. A long white dress
Probably the most important rule in the book. No-one wants to be the girl wearing a white maxi dress to a wedding, unless you're the bride, of course. It's not hard, so don't be selfish about this.
Small side note: it's always wise to carry a little shoulder-coverer such as a stole or a modern blazer, if the wedding is likely to be super formal or in a church. You can whip it off later.
2. White/ivory/cream anything
These days, bridal fashion is so fresh and exciting you may turn up to find the bride wearing a similar white skirt/jumpsuit or even mini dress to you. Prints are fine, but anything in a block bridal colour is a real no-no.
3. Anything see-through
So while the sheer dress trend might be enjoying some popularity, it's not right for a wedding. While Bella Hadid and the whole Dior gang might look staggeringly good with their boxer-briefs on show under a sheer tulle skirt, you'd really be upstaging the bride to appear at her wedding with your knickers out.
That's not to say a little bit of sheer isn't okay. Sheer panels around the upper chest and the legs are okay, so long as you're not revealing anything that wouldn't be considered kosher at a formal event.
4. Anything super low-cut
Again, while the super-duper plunge might work at an evening event, where things tend to get a little racier, it's not wedding appropriate and certainly not if you'll be anywhere near a church.
5. Flip flops
Flip flops are just not wedding attire. Neither are jelly sandals, birkenstocks or trainers. They're all too casual. If you're baring your foot flesh and you're not keen on high heels, think grecian or kitten heeled sandal.
Jeans, besides joggers and pyjama bottoms, are about the most casual of trousers available. So unless your bride has informed you that you'll be mucking in on a farm for her wedding, you'll need to lay off the denim. Smart trousers, if you're not keen on a skirt, are absolutely fine. There are plenty of great formal jumpsuits out there. But how about a palazzo pant with a nice blouse? Drama, volume and the three-quarter versions make room for some really stand-out footwear.
7. Denim of any kind, really
Denim is pretty much on a blanket ban from weddings. Try something in a chiffon or silk instead.
8. A tiara
You are not the bride. You are not participating in some sort of strange pageant. There is little excuse for any woman bar Kate Middleton to be wearing a tiara. They're terribly gauche. But if anyone had any right at all to wear one it would be the woman getting married (though ket's hope she chooses something a little more chic, shall we?).
9. Anything too garish
You can probably work it out for yourselves but this means: animal prints, neon colours, bells and whistles. As much as we actually adore the below Dolce & Gabbana pineapple dress, it's just a little too Carmen Miranda for a wedding. You risk drawing all eyes to you rather than the bridal party, which isn't a very nice thing to do. Prints are fine, in a more muted way, and with less of the ruffles and neon.
10. All over black
Black used to be an absolute faux pas at weddings - you're not at a funeral, after all. The occasion shouldn't be sombre. But a little black trim on an otherwise differently coloured dress is fine. Just be sure to jazz up your accessories with some sparkle and/or colour, to make it clear you're in a mood for revelry rather than sad contemplation!
11. Slogan T-shirts
This isn't 1999 and no one cares that you have Girl Power, or that you like the Rolling Stones, or are monied enough to afford a designer name.
12. Clubbing shoes
There's a difference between shoes for a night out with your girls in a glitzy or dark club, versus the sort of shoe you pair with a classy dress at a wedding. A statement shoe is absolutely fine and we love a metallic shade or even a bit of hardware, but you don't want to look like you're dressed for a night venue rather than a day venue and you definitely want to be able to dance the night away without breaking your ankle.