Details make for perfection but perfection is no detail.
The Jacket
The correct jacket collar height can be determined by ensuring that about half an inch of the shirt collar protrudes from the back. This ensures maximum comfort and aesthetic appeal. There should also be no pulling or bunching up under the collar which is a sign that the collar is pushed up too high.
The collars of a jacket should lie flat against the collar of your shirt not stand away from them. Collars that stand away from the neck produce a “collar gap”, which creates the appearance of the jacket being too large. This is more likely occur with more heavily structured and hard shouldered jackets.
Ideally, there should be no bunching or pulling when the jacket is seen from the rear; there should be sufficient fullness running down the blades of the shoulder and back in order to permit a wide range of movement. Jackets however are not designed to provide a full range of movement. Therefore avoid assuming unusual positions that pull the seams and risk damaging the jacket.
Jacket sleeves should fall vertically from the shoulder or hint at the contours of the arm but should never divot inwardly. Divoting is an obvious indicator that the jacket’s shoulders are too large. Though the shoulder can be “shaved” this is an expensive and difficult alteration.
Lapels should appear to roll towards the chest lying flat and not buckle. Buckling, more often than not, occurs because the jacket is too tight across the chest and distorts its shape.
In the event that a jacket is too tight or too loose it can normally be taken in or let out an inch either side through the back and/or side seams without any significant compromises to its shape.
Trousers
Personal preference and context will dictate the length of one’s trousers.
The most traditional, and therefore conservative, approach is to ensure that the trousers are long to cover and produce a slight break on top of the shoe. The break prevents socks from being revealed when walking while also adding visual heft, and therefore a sense of solemnity. There are dandies with trousers cut so fastidiously that they have breaks that are barely discernible.
Italian peacocks prefer a more contemporary and casual approach: the trousers are cut shorter such that they just hover over the shoe and reveal a sliver of sock. The boldest cut their trouser legs above the shoe such that their socks are always visible.
(photos via. trashness, Schott Schumann, voxtsatoria,unitedarrows, oscarhunt, permanentstyle)