Sometimes all a shirt needs to make it fit perfectly are a couple of well placed darts. Anna from Plan B shows how to add darts to a shirt so it fits your body. (The English translation of her post refers to them as “notches.”) The darts pinch out extra fabric in the just the places where you need the shirt to fit more closely. She use a mannequin to figure the placement and pin the darts. If you don’t have one, you can probably pin the front darts while you’re wearing the shirt. For back darts, you’ll need the help of a friend. Go to Plan B for the tutorial.
[photo from Plan B]