Some of the most basic yoga poses involve lots of arm movement. If you don't have any sleeves, you won't have to worry about constantly pushing them out of your way and can focus instead on your poses. Chose one that doesn't have a plunging neckline and fits your body wella loose shirt or a low neckline will leave you exposed when you bend or twist into a new position. During Bikram or Hot yoga, you will get extremely warm. Women may want to opt for a sports bra in order to stay cool. Sports bras are typically categorized by impact level; a low-impact bra is fine. For men, going shirtless to Bikram is an option. Pick one that is comfortable and fits well. Practice stretching, reaching, and bending your arms to make sure the shirt is not too tight. In inversion poses, your shirt might slide up your torso, so either prepare to tuck it in during class, or wear a camisole underneath. For a more mellow class like Iyengar or Vinyasa, you may want to wear a lightweight sweatshirt over a tank top so you'll be warm at the beginning and end of class when there is less movement. You can always remove layers if you get too hot. During summer, if you're doing yoga outdoors, a swimsuit is perfectly acceptable provided you're comfortable wearing it.

Summary:
Wear a tank top to yoga. Wear a sports bra to a Bikram class. Try a t-shirt. Experiment with layers. Use your swimsuit.