I weigh daily. I make small adjustments to my caloric intake on a daily basis. I use this data to come up with a "calories per pound target" which is then adjusted up or down monthly. This is a lot of work and I do not recommend it. As for fluctuations, you can see a 2 lb. increase or decrease just from your water intake. For some it can be discouraging to see that jump in one day, but I just focus on the long term trend. I keep a simple goal of losing 5 lbs. a month. I also measure body fat to see a more realisitic view of what I am doing. I am currently at an embarrassing 36.2% body fat.
Weigh in will vary. Do what feels comfortable for you.
Male, 5'7", 53.
Start : 04/16/12 - 276.8 lbs.
Today: 06/18/12 - 262.4 lbs.