I weigh once a week. The same day everyweek, first thing in the morning, with nothing on. I find it more accurate than what the dr says. Because you have clothes on which make you weigh more. Also you are heavier in the afternoon than the morning and you cant always go to the dr at the same time. I definatly try not to weigh everyday though which I did at the beginning of my pregnancy. If you are gonna weigh at home though you do need a good scale.
I only do it at the drs office. I figure I am pregnant, and since I use to suffer with anorexia its better for all involved if I don't get caught up on my weight.