Pottery studios recommend wearing comfortable, casual clothing that you don't mind getting clay on. Clay stains wash out of most fabrics with a regular wash cycle, but wear something that won't leave you heartbroken if it gets damaged. Some pottery studios provide aprons, but some advise you to bring your own. Split leg aprons provide the best protection when you're working at a pottery wheel.
Wear a short sleeve shirt or a shirt your can roll up easily to prevent getting your sleeves wet.
Opt for long pants or jeans instead of a skirt or dress. Pants are easier to move in when sitting at a potter's wheel.
Dress in layers, as some studios are colder than others.