1. SEAMS LEGIT
The jacket’s shoulder seams should fall squarely at the edge of your natural shoulder, not short of or beyond it. Make sure to get this one right, or everything else will be thrown off.
2. THE END RESULT
Your sleeve should end right near your wristbone (enough to expose ¼" to ½" of shirt cuff).
3. IT TAKES TWO
When you fasten the top button on a two-button suit, you should be able to fit two horizontal fingers between your chest and the jacket (snug but not pulling). You should also be able to fit two vertical fingers’ worth of room in the waist of your pants when they’re fastened.
4. THE LONG AND SHORT OF IT
The jacket’s bottom hem should fall near the base of your front pockets—just far enough to cover your rear when seen from the back.