Many people want to have a portrait session, but they think they can't because they "have nothing to wear." This is hogwash. First, we are no longer in the days of the Sears photo studio where everyone put on their Sunday best and posed stiffly for photos before a backdrop. The style now is more casual photos, usually taken outdoors.
Second, I think you should wear what you normally wear. After all, that is "you," and the photo should help you remember that moment--who you and your family and loved ones were at that time. Let's not take this "wear what you normally wear" too far, though. Nobody wants to take your photo while you're in a stained undershirt and underwear.
Wear Muted Colors
The clothes you pick for the portrait session shouldn't be too bright. You are "the star" of the photograph, not your clothes. So don't wear anything that takes attention away from you. Photographically speaking, bright colors also have a tendency to reflect their color upon your skin. This can make you look like you're suffering from some ailment.
Do These Pants Make My Butt Look Big?
The tone of the top of your outfit should match the tone of the bottom as close as possible. Lighter colors draw the eye, emphasizing whatever body part they are covering. So, a white top will make your torso appear larger while white pants can emphasize hips and legs (and derriere).
Keep Your Face as the Center of Attention
Generally, people want to see their face in portraits. Of course, there are exceptions, such as athletic portraits, but this list isn’t about those.
Adults should wear tops with sleeves and long pants or a skirt below the knee. Both your arms and your legs have more area than your face, so showing skin on your limbs can draw attention away from the face.
Everyone should wear dark socks and footwear. Again, white tends to draw the eye, so if you show off those new white shoes, don’t be surprised if people notice them more than your face. The exception to this rule is if you are wearing sandals. Don’t wear socks with sandals. Just don’t.
Limit the bling
Jewelry can quickly go from fashionable to gaudy. Some fashionista said once you get ready, look in a mirror and remove one accessory. He or she was right. As a photographer, I can tell you that jewelry can also cause reflections upon part of your body, almost like a laser pointer.
Avoid Fresh Haircuts
I think everyone knows a haircut looks its best a day to a week after it’s actually cut. Speaking of hair, don’t do anything too fancy with it. The less trendy you can be, in both hair and dress, the less dated your portrait will look years down the road.
A couple of tips for groups
If you are getting a photo made with more than one person, you should, of course, try to coordinate your wardrobe. You want to make sure the colors go well together and that you don’t clash.
Solid colors are better than patterns. Patterns make you stand out. I personally think it’s ok for a child (note, I said a child, not children) to wear patterns. They’re smaller size relative to the adults does not distract as much.
Let the photographer know
I like to know what the subjects for the session are going to wear. That helps me pick out a background. For example, if you’re wearing a black shirt, I don’t want to take the photo in front of something dark and have you looking like a disembodied head floating in the middle of the photo.
Or, vice-versa, ask the photographer what he or she is envisioning for your portraits. You will likely want to dress differently for a rural setting than for a background that would be made of brick and metal.
Leave any wardrobe tips that I didn't mention in the comments below.