I weigh myself once a week at the same time and under the same conditions so that I am comparing apples to apples (first thing in the morning, after I use the bathroom but before I eat or drink anything, and no clothes on).
I would drive myself crazy weighing once a day. Weight fluctuates depending on sodium intake, exercise (increased excercise can make you hold onto water), etc.
I also try to focus on my healthy habits instead of the scale. The scale is important, but the healthy behaviors are what get the scale to move down.