Do you know about the rule of thirds? I didn’t. How did I not know about it? Anyway, I do now and I am obsessed. And you will be, too. So listen up.

The rule of thirds is a simple trick that makes you look better, by tweaking your proportions. It is failsafe, it is free, it works on everybody. If you are average height, it makes you look taller. I always wanted to be taller. In fact, in my heart, I believe that I am 5ft 10, like Cindy Crawford, although on the outside I am only 5ft 5½. I’ve never got to the bottom of this mystifying mix-up, but the rule of thirds is a more effective solution than high heels. And it doesn’t just make you look taller, it makes you look better. If you are already tall it makes you look leggier, and whatever height you are it enhances your silhouette, giving you a more supple, fluid line.

Consider this your rule of thirds tutorial. You don’t need any new clothes. You don’t need much time. You don’t need a needle or safety pins or shapewear or, in fact, anything at all, except a full-length mirror. The principle of the rule of thirds is that an image is more appealing if it is divided into one-third and two-thirds than if divided in half. In art and design and architecture, the rule of thirds can be applied horizontally as well as vertically but, for getting dressed, only the vertical concerns us.

It boils down to this. Your outfit should “break” either one-third of the way from your head to your feet, or two-thirds of the way – but not halfway. The break can be created by contrasting colours or anything else that creates a horizontal line (a belt being the obvious example).

The proportions are different on everyone, but as a rule, one-third of the way down your body is somewhere around the top of a pair of high-waisted jeans, a little closer to the bottom of your ribs than to your hipbones. Two-thirds of the way down is going to be somewhere above your knees. To elongate your proportions, all you need to do is create a horizon at one of those two heights. You could do this by tucking your top into your trousers; or it could be pairing an above the knee dress with tall boots.

Take theis lovely outfit abovepictured here. You see how the black top is tucked into the white trousers, creating a punctuation mark that is one-third of the way down the body? That is the rule of thirds in action. Now, imagine if instead of being tucked in, that black top was allowed to hang over the top of the jeans to where it ends at the top of the leg. The rule of thirds gives this outfit energy. Without it, the same clothes would look less dynamic and less interesting. Get it?

The most common way that we break the rule of thirds is with a top or a jacket that falls to hip level over a skirt or trousers. We often talk about clothes in terms of tops and bottoms, which makes it sound as if they should take up equal space on your figure, which breaks the rule of thirds. Sometimes we break the rule by accident: you put your trousers on before you put your jumper on, so the jumper sits on top.

We often break the rule because we mistakenly think it will be more flattering to have a top or jacket long enough to hide a tummy. But tucking a top in isn’t the only way to create a line. If you prefer loose clothing, just wear a top and trousers in the same colour and then add a cropped boxy jacket in a different colour over the top. Everything can be loose and easy, but the colour of the jacket creates a break. Alternatively, place the break two-thirds of the way down your body, by wearing a dress to around knee length without a belt, with boots that end close to your dress hem.

Some rules are meant to be broken. But this one is golden. And if you aren’t already following the rule of thirds, then it is time you took a long hard look in the mirror.

Hair and make up: Sophie Higginson using Davines and Lisa Eldridge beauty. Model: Lily Fofana at Milk. Coat, £109, Zara. Shirt, £160, Samsøe Samsøe. Jumper, £60, Boden. Trousers, £350, Serena . Boots, £70, Schuh