Follow the opening
Fasten the shirt and check the front lies comfortably when you sit. The spacing and placement of buttons affect how the opening behaves between them. A close fit across the chest can create strain even when the waist feels roomy. Compare the whole front rather than choosing a size from one measurement alone.
Fold the cuff
Try the sleeve both as intended and with a simple fold. Notice the bulk at the wrist and whether the cuff closes without pressure. If you usually wear a watch, include it in the fitting. Everyday habits are useful test conditions because they are the conditions the shirt will actually meet.
Feel the inside
Run a hand along the areas that touch the neck and underarm. Seams and labels can feel different after several hours than they do during a quick fitting. A smooth exterior does not tell the whole story of comfort, so take a moment to examine the construction you cannot see in a mirror.
Care for the shape
After washing according to the label, smooth the collar and cuffs while damp. This can make later pressing easier. Avoid treating every shirt identically: a fabric blend, a delicate trim or a particular finish may call for different care even when the overall shape looks familiar.
