I weigh myself on Mondays after the potty break and before I eat anything. I wear whatever I wore to bed the night before since most of my nighties are pretty much the same weight. (I haven't weighed them but I don't really wear heavy stuff to bed).

I try not to weigh myself too early, since for some reason I tend to weigh a little more at say 7 than I do at 9. I try not to peek during the week but, sometimes do. My 'official' weigh in is on mondays though.