The clothes that photograph best are rarely the newest ones. They are the ones that fit, that you can move in, and that you would still be comfortable in an hour later when the light has gone.
Texture over pattern
Linen, wool, denim and lace all catch light in a way that gives a frame depth. Tight patterns and small stripes do the opposite: they fight the grain and, on some fabrics, shimmer unpleasantly once a file is resized.
If several people are being photographed together, agree on a range rather than a uniform — two or three colours that sit near each other, and let everyone pick within it. Matching exactly tends to look like a school photograph.
Wear the thing you already feel like yourself in. It shows, and there is no editing it in later.