Very frequent bathing and washing with previously washed hands - probably three times a day -- with a very mild non-scented soap is recommended. Certainly the whole area of the anatomy should be bathed night and morning and after every bowel movement.
Another precaution the patient can take is to change their underwear once a day, or even more often in hot weather or during menstruation.
But obviously unless the attack is very mild and soon over, get the doctor's advice. He may need a specimen but will tell you about this if so.
It is unfortunate that the subject of cystitis is regarded as being so indelicate a subject. One talks freely enough about infections in the nose and throat, but the other entrances and exits are regarded as being very intimate and unmentionable subjects.
Many articles taken from 'A word with the doctor', by Dr. John Windsor.