Make your biggest clothing investment this year your smartest one.

What constitutes a good investment?  Having recently picked up a new car and lost a conservative £5,000 by simply driving it off the forecourt, I can tell you what isn’t. Indeed, a friend recently enquired about the trade-in value of a car and, after a cursory glance, was told as a goodwill gesture they would offer £200 for scrap. When asked what she felt about that, she replied, “Like crying”.

But the smartest buy a man can make right now, in every sense, is a good coat. There is no risk of tears if you choose wisely and a new coat will soon feel like an old friend, instantly making you feel better about yourself for years to come.

The choices may seem daunting, but in reality the rules are simple. Just think FFS – function, fabric and silhouette. Function is the most straightforward, if only because the right coat should look as good over a suit as worn with a pair of jeans, though in reality you will want to decide whether you are primarily thinking business or pleasure.

Having established the function, your choice of fabric, including colour and pattern, will naturally follow. So, if you want it to be waterproof, you might want to consider something lighter in weight. Cashmere is more luxurious, but potentially less robust, so if you wear your coat with a backpack, the straps might cause bobbling on the shoulders. Darker colours such as black and navy are more adaptable, but camel is always smart, too.

Finally, silhouette. You want a coat to be long enough to comfortably cover the bottom of a suit jacket but not so long that you look like you might be on wheels. The belted option may appear bulkier than a single-breasted coat that finishes below the knee. Do you tend to fill your pockets? (Remember that loose keys and change may well, over time, create holes in the lining.) Finally, as a coat will be worn over other clothes, you probably don’t want something too fitted.

Next year, you’ll go through this whole process again. But don’t worry too much, we all need more than one old friend.

Retro checks in oatmeal, lovat greens or heather tones have their roots in classic British countrywear, originally worn with a side-by-side shotgun cocked over your arm, but the Italians – who love giving an old-school Anglo look a modern twist – show how it is equally at home in town as on the moors. Think of it more like a jacket, especially if in waxed wool, and twin it with a block-colour chunky rollneck. The perfect length should stop just above the knee.

Every man should own a camel coat. The colour flatters all skin tones and works equally well at a wedding as a weekend in the country. The look is always the right side of smooth and a longer double-breasted version will also hide a multitude of sins if your form needs flattering.

When the need for warmth is an important factor, look out for a single-breasted overcoat in a heavier-weight wool. This works well with a discreet pattern such as herringbone or a Donegal fleck. Shorter lapels and a smaller collar are perfect for turning up against the wind.

If you are looking to make a statement, think bigger. Don’t be tempted to mix your messages, however, as you don’t want drama to slip into slapstick. As seen here the look is most effective in dark colours such as black, rather than something louder – there is no need to shout about it when the volume is already turned up. And if you want to wear it with just a T-shirt or fine-gauge knitwear, look out for lighter-weight luxury fabrics such as cashmere that will be incredibly comfortable.

An investment piece doesn’t have to be considered as a stand-alone item. It should also work with your wardrobe. If you do favour a particular colour, think tonally. Twinned with complementary tones of a single colour, your coat can give even a more casual look a sharper edge.

Even a formal coat can work well dressed down, so don’t be afraid to twin it with sportswear. If you want to wear it with a hoodie or a denim jacket, for example, look out for styles with raglan sleeves. Originally designed for Lord Raglan after he lost his arm at the Battle of Waterloo to allow him to use his sword, these allow for greater movement so are comfortable when worn with bulkier pieces underneath.

If colour is your thing, consider a more contemporary claret or maroon, which work brilliantly with denim or looser cut flannels, as here, especially in this shorter, more casual peacoat style. Claret works especially well with blue – just ask the West Ham and Aston Villa fans.

The classic greatcoat traces its roots back to 19th-century military uniforms and its mix of practicality and swagger looks just as good on a modern civilian. Cut to the calf with deep pockets it works hard for the money and will only get better with wear. Here it covers both army and navy worn with another winter classic – the Aran sweater.

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MR PORTER or the products shown_