If I am not trying to lose weight, I tend to weigh myself about once every two weeks or if I feel like I may have been gaining weight. When I am trying to lose weight, I weigh myself every morning, before eating and after using the restroom. I personally find it helpful to see weight fluctuations based on how well I did the previous day, but I make sure to keep in mind that a slight up in weight does not mean that I am failing at my goal! The days that I see a slight increase make me want to work harder, and the days where I see a slight decrease make me feel like it's paying off. That said, I choose one day a week where the weight "matters" to track the overall pattern of my weight. I don't hold myself as accountable as others if I don't weigh daily, but some people do just fine. Likewise, others tend to get obsessive if they weigh daily and for them it's better to space it out.
What has worked best for you so far? Maybe you could try experimenting with different frequencies of weighing to see what helps you best?
Edit: I should also mention, I loosely keep track of my time of the month and *expect* to see a 3-5 pound gain in the days leading up to it, because from experience I know that this is what happens. It actually helps me to have this awareness because I can feel the extra water and if I don't pay attention it makes me want to eat more.