1. Don’t wear your sleeves too short or too long. 1/4” to 1/2” of cuff should show beyond your jacket sleeve.
2. Shirts with button-down collars are not dress shirts. They’re sports shirts, so wear them with a sports coat. Polo players used to button their collars down so they wouldn’t flap up in their face while they played. (Are you beginning to sense a theme here? Fashion rules are largely dictated by what English gentleman and nobility did generations or even centuries ago. Sports coats? You wore them during sport, i.e. hunting. Regimental stripes on ties? They indicated your regiment in the British military. And so on.)
3. If you unbutton your collar, remove your tie. You can wear a suit or sports coat without a tie – just ask Obama – but wearing a tie with an unbuttoned shirt looks sloppy.
4. You can unbutton the top button always (provided you’re not wearing a tie), the second button usually, the third button only on disco night at the Rollerama.