I wash all fabric larger than a charm square in my regular detergent but without fabric softener. I'll either dry it in the drier or hang it, depending on how I feel! I don't iron the material until I'm going to use it. That said, there are a few patterns where you are specifically told not to pre-wash (stack-n-whack, OBW, etc), so those I don't wash, but I know what material I am going to use for them.
With all the chemicals they spray on the fabric in the warehouses to keep the bugs away, I just don't want to work with that...I have asthma and try not to make it worse.