The shoulders of the jacket should be equal to the width of your shoulders. A loose fit will make you look unprofessional. Too narrow, and you won't be able to move your arms.

The jackets should also fit you properly around the waist. There should be enough space to insert two fingers above the button and just tight enough to create a couple of ‘whiskers’ across the front when buttoned up.

Sleeves should be two finger widths past the wrist for shirts, and one and a half fingers for jackets. If you can see the shirt cuff at the wrist, that’s about right..

Trouser legs should have around one crease at the ankle.

It can be tempting to buy a bigger suit to make room for growth, but while an extra inch or two might be all right, more than that will just look terrible

Colour

An easy rule of thumb to follow is: the darker the shade of your suit, the more formal it is. Blue works in most cases.

Solid colours are a safer choice than suits with a pattern.

Black is seen as very formal, and should be reserved for special occasions such as weddings or funerals.

The exact shade can be left to personal taste, but the shirt, jacket, and tie should not be too close in colour. Also, avoid shirts with a colour too close to your skin tone.

Jacket and pants should be from the same set with the same colour and pattern. 

Suit components

There are many components to a suit.

When attending a formal occasion, you need the full complement of jacket, trousers, shirt, tie, belt, and appropriate socks - never white, go for black, navy or dark grey.

You should avoid sneakers, trainers or other canvas shoes, and invest in a smart pair of leather shoes to match your ensemble. If you take care of them, they'll last you for years.

When choosing a tie, it should be no wider than the lapels of the jacket.

A properly tied tie will have a “dimple” or small crease below the knot, and it should reach down to your belt.

Formal wear

Shirts should be tucked in and buttoned to the top.

Never do up the bottom button on your jacket, and remember to undo all buttons when you sit down.

Maintenance tips

• If you want your suit to last a long time, you need to take good care of it. Most suits are dry clean only, so check the label before chucking it in the washing machine.
• Note, however, that dry cleaning your suits can reduce its lifespan because of the chemicals used in the process.
• Another thing to remember is to always wash jacket and pants from the same set together, or they might fade at different rates and end up being different colours.
• Wool will shrink when wet, so avoid being out in the rain when wearing a wool suit.
• Polish your leather shoes to keep them shiny, and take care when you walk so as not to scratch or scuff them.

Accessories

Pocket squares or handkerchiefs are an affordable way to add a pop of colour to your outfit.

Avoid wearing a sports watch. Formal watches should have a leather or metal band.

A backpack is not a suitable bag when you're wearing a suit, both appearance wise (it doesn't look smart), and because the straps will cause the fabric to crease around the shoulders.

Casual wear

If you’re going to a more casual event, you don’t have to wear the full suit. You can leave your tie at home and have the top buttons of your shirt undone. Or if you want, you can swap the suit trousers for a pair of jeans or khaki trousers for a more laid-back look.

Just make sure to check the event's dress code before dressing up.