Picking out wardrobe.
This ties in a great deal to your casting. I am sure you can see why. But, remember the camera is different than real life in that it shows colors, textures and patterns in a different way. Keep it simple and clean no mater what casting you are aiming for.
Bold patterns will be amplified and distract from you. So, do not bring crazy bold patterns for shoot day.
If you are going to wear a t-shirt NO LOGOS or writing should be on them. Polo shirts can naturally have a small logo, but it's better not to have one.
Be aware of the color choices. I won't say no to anything as far as color goes because some people look great in colors of very bright or unusual tones, but ask yourself one question before you prep your clothing... Does it distract from my face? When you are walking down the street it's one thing. When you are on camera it's another. Be aware of the tones. Stay away from overly bright shades. Red can be fine in one shade and disastrous in another. Look in the mirror! Look at what happens to the light around your neck and face. If you get a lot of distortion... don't wear it.
Also, since headshots are in color now that does not mean that you need to wear outlandish colors to get the casting directors attention. The photographs and your communication to the camera will do that.
Bring at least 3 changes of clothing, but I prefer having options so, even if you are only booked for a 3 change shoot, bring enough shirts for more options. I am of the school of thought that it is better to bring "too much" than too little.
Cameras will pick up wrinkles. So, be a pro and make sure that you are dressing with as much care as you would if you were meeting face to face with a casting director for the roll of your life! After all, the whole point of headshots is to promote!
Don't bring any clothing that you know feels weird or sits weird. Chances are it will, at the very least, make you feel weird and that uncomfortable feeling will show up on camera.