Whether a beginning salsa dance class is your first dance class ever, or just your first salsa dance class, you want to be prepared and comfortable so that you can concentrate on the steps and the music. The most important element of your wardrobe will be your shoes. The rest of your outfit will depend slightly on where you are taking class, as they are offered both at dance studios and in night clubs.
The most important consideration for a dance wardrobe is always the shoes. In salsa dancing, you need a shoe that will allow you to turn without gripping the floor. Leather soled shoes are generally the best bet. For men, bring in your dress shoes, and make sure they have a snug fit and don't slip off when you lift your heel. Also, they should not be too pointy or extend much beyond your toe to avoid getting stepped on. Women should choose a shoe with a slight heel, and it should strap on to your ankle; a mule or sandal that you slide into will not work. There are dance shoes that are made specifically for salsa dancing. They are more flexible than regular shoes and have a suede sole that allows you to slide and grip the floor as needed. These should only be used in dance studios. There are also dance sneakers which look a bit more casual than the traditional dance shoe, but give the same benefit.
If the beginning salsa class is offered in a nightclub, which they often are, your attire should be whatever you are comfortable wearing on a night out. Start with the shoe and match your outfit accordingly. Slacks and a nice shirt are good for the men, and the women can either wear nice trousers or a skirt. If you choose a skirt or a dress, remember that you will be spinning around and to take the necessary precautions. Whatever you choose, you should be comfortable moving around in it. Also, you may want to call the club ahead of time; many salsa clubs have dress codes and will not allow things like sneakers or jeans.
The classes that are given in dance studios tend to be a bit more casual. You will see people in sweats or casual exercise attire that allows them to stretch and do more aerobic activity with no constraints. You will also see people wearing what they wore to work that day, and then some who are dressed for a night out. In any case, you should be comfortable and wearing the right shoes. Also, in a studio environment there will most likely be a huge mirror, so you might want to wear something that allows you to see your body. You will be learning how to move your hips, and seeing them move will help out in the learning process.