Put on the waist right side out and pin it together. Place a tape measure, or piece of cotton tape over the garment at the waist line and adjust the fullness at the bottom of the waist. If the shoulder seam lies straight along the top of the shoulder from the base of the neck to the end of the shoulder, if the under-arm seam runs from the center of the under-arm to the waist line slanting a trifle toward the back and the waist is free from wrinkles of any kind with sufficient fullness across the bust, your waist will need no alterations.
If the waist wrinkles from the neck to the bottom of the arm-hole, the shoulder seam slopes too much. Re-pin it, making the seam narrower at the end of the shoulder.
If the waist wrinkles crosswise at the top of the back, or front, it should be altered at the neck and shoulder; cut out the neck a trifle (it is a good plan to make short crosswise cuts across the curve of the neck before cutting out the material) and make the shoulder seam narrower at the end of the shoulder.
Where the waist wrinkles down at the curve of the armseye it should be cut around this curve. It is advisable to make crosswise cuts in the edge, as suggested for the neck, before cutting out the material. If the waist is too loose at under-arm seam, the seam should be taken up until the waist fits smoothly. (Be very careful not to fit it too closely at this point.) If the waist is to be finished with a peplum or band, trim it off the width of a seam below the waist line (be very careful to leave the waist long enough so it will not pull up above the belt of the skirt when the arm is raised).