Getting Started
Preparation
First of all, check with your doctor to make sure that you can handle some sustained exertion. Generally you can control how, ahem, "athletic" things get. But it's easy to get swept up in the moment, so be ready for some sweating and heavy breathing.
Wear comfortable, non-binding clothing. Jeans are a bad choice. Shirts with exposed buttons should be avoided. Clothing with exposed zippers, especially metal zippers, should be avoided. Athletic shirts, t-shirts, sweatshirts, sweatpants, baggy trousers, cargo pants, and yoga pants are all fine. Use your best judgement but you don't want your clothes impeding your movement, or your partner's movement.
Don't wear watches, bracelets, necklaces, dangly things, or bulky rings. If you come with them, put them somewhere safe and out of the way.
Wear practical footwear. Sneakers without excessive cushioning, like skate shoes or trail runners are good choices.
Bring hydration! There are generally fountains around but it's handy to have your own bottle nearby.
Frequently Asked Questions
...or maybe just good questions that we wish someone would ask :D