I think it is suggested by various sources to do one once a month or so, minimum two weeks in between flushes, and after doing a bowel and parasite cleanse.
That said, there are people who do them more frequently and seem to have good results.
The Bowel Cleanse would be important to make sure everything is moving and there are no obstructions, and the parasite cleanse is because most, if not all people have parasites and apparently they can block stones. Therefore it's optimal to do these cleanses first.
I did not and found out after the second flush why it's important to parasite cleanse first.