Wear similar tones of clothing
Think in black and white tones; if everyone wears dark blue and one person wears white, the eye will be drawn to the person wearing white. If there's a reason that one person should stand out, then do it. If not, change your color selections.
Denim in any color for pants and jackets works well. It's classic, it's informal and it comes in lots of great colors. Best of all, it never goes out of style.
Groom your hands and nails; they usually end up in some pictures.
Avoid patterns, logos, branding, and busy designs
Stripes, plaids, checks and busy patterns like paisley all tend to be distracting.
Avoid anything shiny or reflective
Avoid large, shiny objects like belt buckles, bold jewelry and reflective watches.
Unless your watch has a story, it's best to take it off during your portrait session. In fact, it's best to take it off well before you arrive so the marks on your wrist have a chance to fade.
Classic, elegant jewelry like pearls always looks appropriate.
Beware the color red
It attracts attention! If you want to stand out on purpose, wear red. If you choose red for everybody, it's best if the reds match...
Portrait Tips for Women
Wear long sleeves, or at least three-quarter length sleeves.
Choose v-necks, square-necks and turtlenecks.
Avoid cowlnecks and other floppy necklines.
Avoid buttondowns and crewnecks unless you have a very long neck.
Classic jewelry, like pearls, always makes a great choice.
Blouses with collars that open and lie flat look great over a jacket.
Layers look great. A single-breasted jacket over a tight-fit, square-neck top looks fabulous.
Fitted tops always look better than loose-fitting clothing.
No matter what you choose, make sure you can cross your arms comfortably without the shoulders riding up.
Portrait Tips for Men
The more formal the portrait, the darker your colors must be. You can get away with light colors for an informal portrait or location shots in the summer on the beach.
Turtlenecks look great, especially under jackets.
Do not wear a jacket that is much lighter than what you're wearing underneath it.
Crewnecks sweaters or layers work fine on men. Don't be afraid to wear white t-shirts under buttondown shirts.
Portrait Tips for Children
Dress kids in similar tones. Even though kids may be attached to their superhero t-shirts, let them wear them to the portrait session, just not during it!
Kids can get away with brighter colors and patterns, but avoid logos and branding.