Comfortable shoes and comfortable clothes.
The long answer is that you should wear shoes that you will still feel comfortable in after dance for hours. Most people find it difficult to swing dance in shoes that easily fly off. The floors we dance on appreciate clean-soled shoes. If you don’t have shoes to change into, please check the bottoms of your shoes for gravel and grit that can damage the floor.
Clothes that move and breathe are your best bet. Clothes that you can stretch out your legs, raise your arms above your head, and just plain move comfortably.
As for style, again, wear what you are comfortable in. If you are most comfortable in casual clothes, dress casually. If you are most comfortable in a suit, wear a suit. People tend to dress more casually during the week and sharper for the weekend dances.
Music that inspires you to dance. For us that is music primarily from the 1930s & 40s or more recent but with a similar feeling. Sometimes it is fun to deviate from the norm, for instance the Beatles song “When I’m Sixty-Four” can be a lot of fun to dance to. Some people like to try to swing dance to just about anything, but we tend to be inspired more by traditional sounding swing.