I weigh myself twice a day. 1 - 2 times in the morning, 1 - 2 times in the evening. It sounds excessive, but I gained 100 lbs in ten years, so it helps keep me accountable and on track.
I weigh myself twice a week. Sunday morning and Wednesday mornings. I only record what I weigh on Sundays, but check my weight on Wed to see if I'm on track, or if I'm in a stall.