What you wear in your photo is very important. I highly recommend you take some time to prepare your wardrobe. The clothes should reflect your profession or business. Generally lawyers need a suit/tie and free lance artists can certainly look more relaxed.
Darker colours shoot better! Avoid light earthy tones such a beige a brown. Unless under a blazer or jacket I would avoid white. Black is OK, but navy and charcoal is preferable. Small patterns and smaller strpies work well and generally blue is flattering to everyone. If you are shooting with just a shirt I recommend darker than lighter.
If you are wearing a suit or blazer and I recommend everyone bring a jacket in a darker colour, please bring the one that fits you best and you are able to do the top button without creasing the lapel.
Collars and Ties
If you are wearing a tie, the shirt should generally be neutral. The tie understated with small or low key patterns so as to not attract too much attention. It is important that you wear a shirt with a more relaxed collar. I tend to shoot the pose with a body angle left or right to the camera and your face turned to face the camera. This puts a skight twist to your neck and if your collar is too tight it will squeeze the neck causing skin to hang over the edge of the collar. This is very difficult to fix in post retouching work.
Choose a ties with fabric that knots perfectly and is not too big or small. The knot should tie up to the collar snugly.