These are the six key points you should look at for a new shirt to fit perfectly:
 

(1) Length of Arms

The length of the arms of a shirt is perfect when the cuff covers the wrists.
 

(2) Shirt Sleeves

At least half an inch (1 cm) of the shirt cuff should show under the jacket sleeves
 

(3) Tips of Shirt Collar

The tips of the well-cutt collar touch the breast of the shirt and will not lift up.
 

(4) Edge of Shirt Collar

The outer edge of the collar and its tips should just be covered by the lapel of the jacket.
 

(5) Height of Shirt Collar

The height of the shirt collar should not be covered by the jacket at the back of the neck.
 

(6) Knot of Necktie

The knot of the necktie should sit exactly in the triangle between the two sides of the collar.