Monkey, first of all, congratulations! It's a big step but it's so beautiful to share your life with someone else...
I am from Brasil so I will go for what I know about there... don't know where you are now, UK or USA, but... you might have what we call "spa for brides/grooms", which you pay a certain amount and spend the day there, receiving relaxing massages, taking baths, and then later on (if you are a woman) getting the make up and everything.
If you don't have these kind of places close to you, or you can't afford it, then it depends on what makes you feel relaxed. For example, I would light an incense, try some meditation with new age music in the background... have some herbal calming tea... but it might not be your cuppa, so, I'd go for what usually makes you feel relaxed in your normal days? playing a game? reading a book? something that will keep you distracted enough not to think soooo much about the wedding!
Hope it helped! Good luck and be happy!