Beginners often ask us what they should wear to class. In our information booklet we say that they should wear comfortable exercise clothes. Some rock up in baggy t-shirts over baggy pants, other wear skin tight, and some arrive in their work clothes. Ultimately, you can't tell someone what to wear, but you can advise on what clothing works best and why.
You want to be able to move freely. Thus, I advise wearing stretch fabric pants and shirt. Wearing stiff fabrics, like cotton shirts and jeans, restricts your movement and is rather uncomfortable. Wearing cotton knits are both comfortable and flexible enough to move with your body. It's also cooler than synthetics such as lycra.
It's best to wear fitted clothes rather than baggy. The fitted clothes will allow both you and your teacher to be able to see your movements better. Baggy clothes hide your body making it difficult for you and your teacher to judge whether you have correct posture and are doing the move or combination correctly. I prefer it when my students wear pants that fitted around the knees (like yoga pants) and fitted tanks. I can see their posture, knees and movements much better. If they are wearing jeans and a t-shirt, I can't tell they are sinking into their hips or if they have locked their knees.
I don't look good in yoga pants, but I wear them in class anyway. My students (and myself) can see my body. Without a proper model, it makes it near impossible for the students to learn. I also personally prefer wearing tanks tops to sleeved fitted t-shirts. I find the sleeves hinder my shoulder movement and tend to ride up on my arms irritating me.Wearing clothes that are too tight is also not advisable. It restricts your movements, and it will ride up and make you rather uncomfortable.
When it comes to scarves or belts, I think it is fine for a beginner to wear a coined hip scarf. The sounds can help with learning and makes them feel like a belly dancer. However, once you move up to an intermediate level and above, the coins must go. I will allow it if we are doing a shimmy drill and I want to hear the sound to ensure that everyone is in time, but otherwise ... no. They become a distraction and a headache. Especially when practicing zills/sagat. There are so many beautiful non-coin belts to choose from. I have a red gypsy style one that I love to use in an everyday class as well as a pink sparkly one (strangely enough I'm not a pink sparkly person, but I like this scarf), and several black and brown ones. In South Africa you can find cheap ones at Chinese clothing stores (I got my pink sparkly scarf at one near my house). You can also make your own, put your own personality in it. Much nicer than a plain old coin scarf.
Finally, your feet. Belly dance is best done barefoot. However, sometimes it's too cold or the floor you are dancing on isn't great. I have a pair of split sole ballet shoes for such occasions. If my feet are cold to start, I will wear them until they have warmed up. At some workshops the venue's floor is rough or very unclean. I will then also wear my ballet shoes. Melanie has elastosplit shoes made by Bloch. They have a much more natural feel to them and don't hinder foot movement.
There are many different styles of dance shoes to choose from. Make sure that they are properly fitted to your foot, are comfortable and allow freedom of movement.
What you wear to class can make a difference. If you are uncomfortable, you won't be able to concentrate on what you are doing. If you and your teacher can't see your movements then you are probably not getting the adjustment and correction you need. So next time you are going to a class or workshop, think about you are wearing.