A suit that fits well starts and ends at the shoulders. It is the one part of a jacket that cannot be meaningfully altered without remaking the garment, so it is the first thing a tailor checks, and the first thing worth checking yourself before anything else.

Stand in front of a mirror with the jacket buttoned. The seam where sleeve meets shoulder should sit exactly at the edge of your shoulder bone, not out past it and not pulling in from it. If it is wrong there, very little else about the fit can be corrected, however good the rest of the alteration.

Everything below the shoulder line is fair territory for a skilled tailor. Sleeve length can be shortened from the cuff. The waist can be taken in at the side seams for a cleaner line through the body. Trouser length is the most common alteration of all, and one that most people leave slightly too long out of habit rather than choice – a trouser that breaks once, lightly, at the shoe reads far sharper than one pooling at the ankle.

Jacket length is more constrained. It can be shortened a little, but taking more than a centimetre or two off usually disturbs the proportion between jacket and trouser, and a good tailor will say so rather than simply doing what is asked.

The honest test of any suit is not how it looks standing straight, but how it moves – raise your arms, sit down, turn at the waist. A jacket that fits well allows all of that without pulling across the back or gaping at the chest. Our alterations team fit every suit this way before a single pin goes in, because a suit is worn, not just looked at.