You've seen the name-brand yoga outfits advertised, especially the ones from organic material. Do you really need that to practice yoga? While the short answer is no, there may be more to consider than just your comfort when dressing to practice. Bare feet are the norm when practicing yoga, but if you have issues with your feet you might want to check with your doctor and your teacher about other options.
If you're on your own, the best thing to think about when considering an outfit is comfort and freedom of movement. Jeans are not a good idea since they generally constrict how far you can move, but sweats might make you too warm in a challenging program. Shorts and a t-shirt might also be too chilly if you have a static practice ahead of you with poses that are easily within your grasp.
If you're in class, you should also think about the types of positions you might get into, like turning up-side down, which might expose more skin than you intend if you wear a baggy shirt. Also, your teacher might not be able to see your movements. That increases the likelihood that he or she will have to spend more time to see you properly and correct you if necessary. If you're hiding in the back in a lot of loose clothing, the teacher might decide you prefer not to be corrected.
The choice becomes what is needed from an outfit. If you're a class regular, it may be worth investing in clothes suited specifically to yoga like a semi-form-fitting top and pants or even a one-piece unitard. This gives your teacher, and you if the room has mirrors, a great view of the pose and allows easy corrections. If you're trying it out for the first time, it is better to grab something in case you decide yoga just isn't for you.
If you're at home, comfort is always the top priority. Make sure whichever option you decide is best for you doesn't restrict your movement in any way. For the serious practitioner who follows all the branches of yoga, there may be no better choice than the organic options offered by so many yoga clothing companies. Be certain you can manage different poses before purchasing, and while checking also to see if inner tags will bother you or if that shirt requires you to pull it down every time you lift your arms over your head. Adjusting your clothing during practice is something you definitely want to avoid.
After you've decided on the clothing options, consider removing jewelry or accessories. A watch may or may not be an issue, but if it cuts into your wrist or distracts you to check the time it should stay home. Stud earrings are the best if you need to wear them; dangling parts might get caught in your hair and the sound and movement is distracting. Necklaces can get caught from moving around, and bracelets often have to be adjusted when you move. Rings can also be a problem when many poses require you to balance a good portion of your weight on your hands. The best recommendation is to remove all accessories and jewelry, except one tie for your hair to stay out of your face or even pull it back in a ponytail or a braid if it's long. Consider washing off any make-up before practice, if and when you get sweaty it will annoy you.
Keep in mind your purpose for yoga when you decide what to wear to a yoga class or a home practice. Get the most out of your experience by keeping distractions to a minimum.