Taking in Shoulders. Alterations to the shoulders can be quite difficult. Shoulders tend to stay stable when an individual is fully grown, so this is a onetime alteration. Fine is you have a particular jacket that you simply have to adapt to your frame, but most people but the cloths to suit the shoulders and other unchanging parts of their frame and adapt the other features.
Altering Sides. If you don’t but to fit your shoulders you are probably buying to fit your widest point. If a top garment otherwise fits but is snug or very loose at some point in the middle you can usually alter it about one size up or down, This is useful for those who want to keep a wardrobe after gaining of losing weight.
Altering Sleeve Length. A fairly common procedure. Not unusual for an otherwise ideal garment to fit well except for the sleeves. Given the low cost of a sleeve shortening one should not hesitate to buy and modify something that is otherwise well suited.
Altering Pants legs. If you buy to accommodate the width of your thighs the pants are generally modifiable in terms of leg length and waist. It is easy to take in the waist, and probably flattering, but difficult to modify the middle of the leg.
Skirt Hem lines. An easy undertaking, but totally up to personal taste and build. Women can set the length to make their legs look longer. A bit of experimentation with something to hold the hemline in place can give a good idea of what works best.
The extent that a piece of clothing can be modified is set by the amount of available material. More expensive clothes tend to accommodate change better than bargain buys, but sometime an inexpensive item can work.
Buy so that hardest to alter part of the garment fits well. For jackets this means the shoulders; for pants this is the width of the thigh.
While it is possible to reduce a garment in all dimensions it is ill advised. Not only is it expensive (and cheaper to buy in a different size) but proportions tend to be lost as a garment shrinks. Large pockets on a smaller suit look disproportionate.