Me?
First thing in the morning. Naked. After going to the bathroom but before taking a shower or exercising (I don't want to count sweating as weight loss, and I don't want to weigh wet hair).
I won't weigh after I've had anything to eat or drink. I won't weight later in the day. (Although I sometimes weigh for fun right before going to bed. I lose about 3 pounds while I sleep. The evening weight is never recorded, though.)
How about you guys? What's your scale routine?