How dry does my wood need to be?

Your wood needs to be less than 10% moisture.  For the best results, it should be oven dry or 0% moisture.  The only way you will get to 0% is to artificially dry your wood.  Even wood that has been sitting in your barn for 25 years will have moisture in it due to ambient humidity.  I place all of my wood in my oven at 220° F for 24 hours minimum to get it to 0%.  You may be able to dry them for less time but I don't like taking the time to keep weighing it to see when it has stopped loosing weight so I go 24 hours at least.  Bigger pieces will take longer.  Then, when you take them out of the oven, immediately place them in a ziplock bag and seal them up to cool down.  This will prevent the hot, super dry wood from immediately starting to pick up moisture from the air as it cools.  A side benefit is that if your wood does still have moisture in it, it will usually show up as condensation on the inside of the bag and you will know they were not at 0%!