Birch firewood is always best stored in a well ventilated and dry location.
If storing firewood outside make sure it is off the ground so no ground moisture seeps into the wood causing mold or rot. Put a wooden pallet down first and stack your firewood on top of it. Make sure to cover the top to keep moisture out.
Inside storage is a little easier. Bring the firewood inside the house at least 24 hours ahead of time to make sure it is thawed and dry before burning. Store inside on a rack. Try to keep it from directly resting on the ground. Good air flow around your wood is ideal. And of course, even inside, keep it dry.