Things to Avoid When Shooting Portraits..

When I say things I mean things from types of wardrobe, accessories, types of makeup, etc.. The following are general rules you want to avoid for most types of portrait photography.

1. Reflective Material/Surfaces
1. Unless you want the reflected light on the photo and causing some flare. This tends to cause a lot of distraction from the primary subjects which should always be the eyes of the person(s).
2. Makeup, Wardrobe, and Accessories may have reflective material/surfaces so ensure you as the model to not bring them along unless specifically told or if you're a photographer ensure the person(s) you're shooting to not bring those types of items.
2. Logos
1. Unless you have permission to shoot the logos displayed on the wardrobe and accessories don't intentionally shoot people with logos on their wardrobe or accessories. Photographers ensure person(s) you're shooting to not bring wardrobe and accessories with logos to avoid legal issues either today or anytime in the future. (I'm not a lawyer, copyright/patents/trademark laws diff in different countries)
3. Patterns and Designs
1. Some patterns like boxes, stripes will Morie, which will cause issues photographing the patterns and cause artificial coloring. 
2. Other patterns will just generally be distracting from the eyes, which should always be your goal to avoid and keep the photo's primary focus are the eyes of the person for most types of portraits expect fashion photography generally.
3. As for unique designs, you would generally want to also avoid as many of them are trademarked, patented, copyrighted. (Again I'm not a lawyer, copyright/patents/trademark laws diff in different countries) You may be able to get away with universal designs like flowers...
4. Neon Colors
1. You should always avoid neon colors because the focus in a color portrait will have the viewer focus first on that color than the color of the eyes and the person.

Check out related articles on Model Photographer Tips Series - Index and Models and Photographers Tip Series - Index.