There has been a thread on this on the SW off topic forum which you could search for. Some of it was sensible and some of it was very funny !
I would suggest that you try and do things the same as far as possible from week to week. So wear the same clothes (until you grow out of them !), try to eat and drink normally but if possible try to eat similar things during that day from week to week. Your weight will be more consistent then. At the end of the day, if you starve yourself/dehydrate yourself for the day you may weigh less that week than you would have done but then you will either regain that the following week if you eat normally or have to do the same every week *eeek* !
I'm sure there are lots of opinions on this one though.