You should be able to fit a single finger between your neck and the collar of your shirt, but no more than that.
A small amount of shirt collar should be visible above the jacket.
Your shirt collar should complement your face as well as the kind of knot you tie in your neck wear.
If you’re going without a tie entirely, keep the collar on the smaller side.
If you’re wearing a watch with your business or dress shirt, make sure it’s something elegant and sophisticated, not the bulky, shock-resistant number you wear playing golf.
Nothing ruins a stylish look like a cascade of wrinkles. Iron your shirt carefully.