Yoga is done in bare feet on a yoga mat. Even the most basic yoga stretches require clothes that can stretch or move, so wear the most comfortable outfit that allows you to move around easily. If you’re doing a gentle, slower class then dress warm (sweat pants, long sleeve shirt) and if it’s a more rigorous class wear shorts and a t-shirt or a tank top. Teachers will often suggest that you leave your ego at the door, and that includes not being self-conscious about the clothes you are wearing. Wear what makes you feel good.