A tiny bit of information that might be helpful is to use something that will give your hands "grip". There are a dozen things that you can try. Some folks use office rubber fingers, some gloves made for FMQ, some use garden gloves, some use a lotion.
Don't FMQ for too long a period before taking a break. Get up and walk around a little bit to rest your eyes, arms and back. If you feel yourself tensing up when your are FMQing, take a couple of really deep breaths.