Buy a tunic, ditch daytime black and save your jewellery for fat days: How to look fabulous after 50 - by the Vogue editor who dressed Diana

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As an editor at Vogue I’ve spent the whole of my life in fashion. I helped Diana, Princess of Wales develop her own style and then went on to oversee the launch of Vogue in Russia, India and the Netherlands.

So you’d think I’d know a thing or two about dressing. But when I hit 50 I found I had to reconsider what to wear.

We all change shape as we age and however hard it might be, we have to take a good look at our new body shape and accept what we see. There will no doubt be a period of mourning for your younger self, but you’ve got to get over it.

Fashion tips: Princess Diana with Anna Harvey at a catwalk fashion show in 1995 

Know when to phase out certain wardrobe favourites — I believe, for example, that at 72 the age for a mini skirt and thigh boots is well and truly over for me, and, as a general rule, a plunging decollete looks a tiny bit desperate after 60.

But some of my cast-iron rules such as ‘no leggings’ have mellowed. And I carried on wearing a bikini into my 50s if I was by the pool.

The key is to avoid wearing what you’ve always worn. In the same way that it’s all too easy to convince yourself you’ll never drink Earl Grey or you hate musicals, only to miraculously discover you don’t at all, one can also build up a set of self-rules about clothes that actually you haven’t taken out and shaken down for years — I can’t wear trousers/skirts; I never wear blue, and so on.

It took a long time for Princess Diana’s own style to evolve, but when it did, it was pretty near perfect in my opinion. She knew her figure and had the advantage of being able to see herself in pictures all the time, so she could correct everything that she did wrong the day before.

I know Diana would have looked amazing in her 50s. I’m quite sure she’d have been an icon to all us older ladies now. I very much doubt you’d see her in black leather, though I may be wrong. No one wants to hear that stage whisper ‘mutton’ — heaven forbid!

After a certain age, fashion doesn’t matter — it’s style that counts, and that is eminently achievable and not difficult if you follow these rules ...

Ageing gracefully: Model Carmen Dell’Orefice (centre), 85, in faux fur scarf, £130 and dress, £242, both airfield.at

Be brutally honest about your shape

Rule one is to become familiar with the way your body is right now. Next time you go clothes shopping, make the most of the changing rooms. Strip off, use the mirrors — all of them!

Look at yourself from the front, side and back. That’s where you see the unpalatable truths — the floppy bits, the tummy and thigh bulges, the things other people may notice when you walk into a room.

And check out the back view — under-arm and bra bulges, a stoop of the shoulders and, of course, your bottom! Test out your posture, too, and notice how much better you look when your shoulders are not sloped and your back is straight.

We all change shape as we age — our metabolism slows with age, and there is also the menopausal change in hormone levels — and although that does not necessarily mean getting larger, many of us do just that, particularly round the middle.

As far as the tummy is concerned, by a certain age most people have lost some muscle tone — anyone who has had a child particularly — and some of the elasticity of your stomach muscles will have gone.

There is definitely a psychological barrier to accepting you might be a size larger than you used to be, but just because you can squeeze into your usual size, it doesn’t mean you still look good in it.

Save jewellery for fat days

When you’re feeling self conscious about your chins and saggy bits and so on, wear an amazing necklace and people will look straight at that, not at you.

I consider earrings to be as important as mascara — and whether they are semi-precious drop earrings, classic small gold hoops, diamond studs, or of course pearl, which can, almost literally, light up your face, they will always attract attention in a good way.

When you’re feeling self conscious about your chins and saggy bits and so on, wear an amazing necklace and people will look straight at that, not at you. Pictured, fringe earrings, £15.99, mango.com

Insist on dresses with sleeves

Whenever I go into a shop, I walk around once, very fast, to see how many things hanging on the rails have sleeves. If there is nothing, I walk out again. Some stores don’t even stock cardigans.

I buy my cardigans separately — mostly cheap and mostly from Uniqlo, cotton in the summer, cashmere in the winter.

Personally I prefer ones that button to the neck — V-neck ones are slightly more difficult to work with dress necklines; they look better worn with round necks or shirts.

Ditch black during the day

Try not to wear too much black during the day — it is so ageing; instead try grey, light or dark, or neutrals. And not too much white or cream, other than as a T-shirt or shirt. Navy blue is softer, warmer than black, and I think much nicer. Brown, too, in all its tones, is a much underrated palette — chestnut, caramel, chocolate, both milk and plain are flattering shades for every skin shade.

In the evening, don’t ignore jewel and berry colours — sapphire, garnet, emerald; blackberry, raspberry, blueberry and damson — which can be very pretty on older skin in the evening light.

If in doubt wear a tunic

The tunic shape is the ultimate forgiving outline. I discovered it when I worked for Vogue India. You can wear a tunic as a top or a dress or over a straight skirt.

The essential thing is that it should be neat across the shoulders and with a straight, set-in sleeve rather than a kimono-shaped sleeve, so that you look small on top with an elongated body.

Any tunic should finish at crotch level at the very least and if you are self-conscious about your bottom or hips, look for a tunic length that drops to thigh level.

The tunic shape is the ultimate forgiving outline. I discovered it when I worked for Vogue India. Pictured, cashmere tunic, £175, lkbennett.com

Big knickers do work

They may be neither very attractive nor sexy, but they leave the minimum of VPL (visible panty line).

If you’re like me who has a dropped bottom, that means that rather than cutting in under your bottom, which in itself doesn’t look that good, the VPL can cut through bottom sag in a most unattractive way. Under full or soft skirts you can, of course, wear anything you like, but under a straight skirt or tight trousers you definitely do need some sort of support underwear.

And a good bra really is an absolute necessity. It should not sit too low, but neither should it sit too high, and there should be no bulges at the back, nor at the sides beneath the armpits. Under wiring is not essential, but always buy a bra that is moulded or lined.

Follow grown-up skirt rules

Wear a skirt length that either sits on the knee or just below. Pictured, belted skirt, £45, warehouse.com

Wear a skirt length that either sits on the knee or just below, although that said, if your knees still look ok, a skirt that finishes just above them can work, especially if it is made in a good, not too flimsy material — and if, in the winter, you wear opaque tights, preferably black.

Long skirts should not be straight; this is not a good look. Go for a softer, flowing silhouette — perhaps a soft skirt that grazes the upper calf.

The pleats on a pleated skirt should not fall directly from the waistband, unless you are exceptionally slim or well under 40 — this will instantly highlight a tummy bulge. Never combine an A-line skirt with an A-line top — you will look like a triangle on legs. Team your skirt with neat tops — a fitted T-shirt or jumper, ideally tucked in. If your skirt ends just below the knee a flat shoe is possible, but you will usually look and feel more elegant in a medium heel; this is also a style where boots always work, whatever the length of the skirt.

Avoid these dress mistakes

If your dress has a waist, is it too short-waisted for your height?

A dress that sits much above your natural waistline can make you look pregnant and out of proportion.

Body-con and tight-fitting shift dresses, unless they are cleverly made, are difficult to wear after a certain age.

They only work if they are made in a fabric such as double jersey and if they have gathers or ruching at both front and back. The shift, meanwhile, must not touch the body or it will ride up when you are sitting and standing. And don’t forget the benefits of a lightweight, long cardigan to soften the line over the tummy.

Another shape that is deservedly still popular is the wrap dress — the shape that Diane von Furstenberg first designed and introduced in 1974.

The gathers hide the tummy and the V-neck is always flattering.

If your dress has a waist, is it too short-waisted for your height? Pictured, tie-waist dress, £39, johnlewis. com

Yes, you can wear a biker jacket

It may not be everyone’s first choice when thinking about jackets, but if worn in a fabric — rather than chrome-studded and buckled black leather — I rather like the biker shape.

Box or short jackets work far better over dresses and skirts than trousers — personally with trousers I always wear a longer jacket to cover my rear. Or one of the most versatile of evening jackets is a black tuxedo. It oozes style.

Box or short jackets work far better over dresses and skirts than trousers. Pictured, biker, £195, warehouse. com

Beware skinny jeans

Skinny jeans are not your style if you have either big hips or tummy or wide calves. Tighter jeans seem to come with low or medium rise waistlines, a disaster for the tummied-ones among us. High-rise are the best. Always a flattering cut, bootcut jeans are good for balancing out slightly heavier hips or bust; look for a medium or high-rise pair.

Do this foolproof jacket test

When you try a jacket for the first time, bring both hands forward to test the fit across the back and shoulders. If it pulls uncomfortably or starts to wrinkle under the arms, it is too tight and will not hang properly. There are many good coats on the High Street — the key is to find one as simple as possible and comparatively muted in colour. It’s the fancy buttons and belts — that make a coat look cheap.

TAKE A GOOD LOOK AT YOUR BODY SHAPE AND ACCEPT WHAT YOU SEE

Roll-neck, £95, reiss.com

Skirt, £400, dorothee-schumacher.com.

Shoes (for all outfits), £175, lkbennett.com

Earrings, £120, dinnyhall.com

Pink coat, £225, topshop.com

Shirt, £39.99, zara.com

Trousers, £330, dorothee-schumacher.com

Knit tunic, £29.99, zara.com

White shirt, £59, hobbs.co.uk.

Burgundy trousers, £25, topshop.com

Shiny tights make legs look fat

I buy opaque tights a size larger than usual so that the colour is even all over the leg, rather than becoming paler where they are being stretched. Tights with a shine tend to make the legs look fatter, whereas matt tights make them look slimmer. If your style is a bit boho, then, I think, coloured tights can be fun. Sometimes. But while striped, lacy or decorative tights look great on the young, by the age of 50, be careful.

What not to buy on the High Street

I’m always in and out of Topshop, H&M, Zara and Cos, but I would never buy smart trousers, a white silk shirt or a tuxedo jacket there. Cheap see-through shirts are not a good look.

Cheap trousers, unless they’re summer holiday trousers like palazzo pants or printed trousers are also a mistake. They look wonderful in the shop and then you sit down and in no time they crease behind the knees and across the hips.

And finally...

The easiest way to look older is to dress ‘younger’. Just don’t do it. If you’re asking yourself, ‘does this make me look younger’, you’ve lost sight of what it means to be stylish.

• Adapted by Liz Hoggard from Timeless Style by Anna Harvey (Double-Barrelled Books £24.95). To order a copy for £18.70 (20 per cent discount) visit mailbookshop.co.uk or call 0844 571 0640, p&p is free on orders over £15. Offer valid until November 21, 2016.