Solid black will under expose, and with no detail on the clothing, it will look funny, like it was inked-out. Bright white can also have problems, though I’ve had less trouble with it. However, if there was an over-exposure with white, it would be worse than the problems with black.
It's best to wear things that are well in the middle range. Neither too dark nor too light, middle tones come out the best.
Cloth with texture, such as a print or pattern, is less subject to the inking-out problem.
This is the one thing you really must get down perfectly, as a model. The light is always in your face! If it’s not, the photographer will add reflectors or more lights, to make it so!
Look at the samples on the left. In the top one, the model was squinting. In the bottom, her eyes are open. The top one not only covers the eyes, but puts what does show into deep shadow. In addition, it adds lines around the eyes. In the lower one, she has beautiful eyes, and you can see them.
So keep your eyes open. It can make or break a good photo.
It’s normal for you to bring someone along. You’ll want someone to help out, to hold things and whatnot. In addition to helping you, I’ll need some help too; specifically, holding reflectors.
One time I was doing a shoot with someone who had brought her whole family along. That was very nice, as they helped keep her distracted and relaxed.