It's totally up to you. (But long pants and sweaters aren't recommended for good results!) Some people choose to tan in their bathing suits or underwear, and others prefer a more "natural" approach. Since you are in a private room while tanning, you can wear whatever you like. The only thing required is that you do wear eye protection every time you tan, because eyes are unable to protect themselves from UV light, even when they are closed, and the light can cause temporary and permanent damage to them. Many different eye protection options are available at all tanning facilities. If you are tanning a previously unexposed part of your body, be sure to cover it up for part of your tanning time, so it can catch up safely with the rest of your tan. Wearing some garments can leave you with white patches, which are good for 'monitoring' the amount of tanning.