Looking good at a best friend's wedding is all about getting the balance right. The key is to look smart and stylish without overshadowing the bride

Rule number 1: Be prepared

Don't leave finding a wedding outfit to the last minute. Do your research, using magazines and the internet as a starting point. If buying online, be sure to allow enough time for delivery (and return) of goods.

On the high street, don't just stick to the usual suspects. Set aside a day (and get there early before the crowds) to investigate new boutiques and some of the larger department stores, you may be pleasantly surprised.

Rule number 2: Ask the experts

Think about using a personal shopper it'll be just like having your very own stylist! Topshop's style advisor service offers a 'truly hassle-free experience,' you even get to jump the queues and use the VIP fitting rooms.

John Lewis has trained fashion advisors so, while they're trawling the shop floor for that perfect little ensemble, you can nip upstairs and sort out the wedding gift! And Debenhams' personal shoppers will help 'guide you through the trends' and co-ordinate outfits for the whole wedding entourage.

Rule number 3: Get it right

Wear something that shows you're taking the occasion seriously. The idea is to look like the very best version of you. So play it smart. Both guest and clothes should be on their best behaviour.

Always follow the dress code. Bride-to-be Harriet Margolies found a gorgeous floor-length purple Amanda Wakeley dress and then sensibly informed guests not to wear 'either purple or floor-length dresses' on the wedding invite.

'I'm not going to be wearing a traditional white dress so we decided to tell people,' she says. 'I found something really special, and we just wanted to save everybody from embarrassment.'

Rule number 4: what not to wear

Don't wear anything to cleavage-y or too short. The wedding guests will be a mixture of different age groups, friends and family of the bride and groom, and we don't want to give granddad a heart attack! Go for a demure look.

This may be stating the obvious but head-to-toe white is a no-no.

Now, black maybe OK for the boys' tuxedos but it just looks a bit harsh at a summer wedding. Go for navy blue instead.

Rule number 5: be prepared (part deux)

A wedding is the perfect excuse to buy some new underwear. Let's face it, a tatty old grey bra under a gorgeous new frock is never a good look. Take the outfit along when shopping for undies, this will help you make the right choice.