Collars that are overly tight cause the neck to bulge above the collar and detract from a great looking headshot. Pay close attention to your collar choice. A smooth wrinkle free collar looks best. A little extra starch and collar stays can make a world of difference. It may be a bit uncomfortable for a daily choice but for a clean sharp looking portrait it is worth the moments of a little discomfort in order to create a great headshot that reflects on your personal brand. Some button-down collars tend to create wrinkles that detract from that clean look so chose one with care if you are committed to them.
When choosing a shirt that you will wear with a tie chose a collar that is the right size and fits your neck. If once buttoning shirt the collar is too tight or too loose it will adversely affect the overall appeal of the headshot or portrait. If the collar is too tight your neck will bulge out above it and if it is too loose the open space will make you look unfinished. Make sure that you can button the collar easily and that your tie choice, as far as size, matches the space between the two wings of you collar.
Choose a tie knot that fits the opening between the collars wings. A Winsor knot has a very symmetrical look but can be bulky with heavy tie materials. A four-and-hand tie knot can work well with broader ties and with ties of heavier material but needs attention to its positioning to keep it looking sharp. Also make sure the knot is sung up tight enough to cover the button of the collar if only for the few moments of the photograph. We want nothing to detract from the overall look of a high quality well finished professional.