Dim the lights to turn your focus inward
Clean up the room, put things in their place, and ensure there is a clear, unobstructed path to the washroom
Ask any roommates to kindly refrain from entering the room before, during, and just after the experience (unless they are required to do as a Peer Monitor, in which case just asking them to remain quiet when doing so)
Keep any pets or children out of the room during the experience
Wear comfortable, loose-fitting clothing
Add your own comforting touches, such as an eye mask, calming scents, any sentimental or important items that help create a calm, open environment
More here.