There are various kinds of urinary stones (e.g., calcium oxalate stones, struvite stones). What is good for one kind of urinary stone, may make another worse. Therefore one can say little about prevention. Here are some tips that have general validity:
Stimulate fluid intake (for example, offer more wet food, milk for cats, pudding, yoghurt, various water types and drinking vessels, offer GimCat ShinyCat Snacks)
Feed high quality egg whites (eg ShinyCat)
Do not feed too much vitamin D
Feed several small meals a day
There are studies that show that well digestible, energetic food increases the amount of fluid intake. Furthermore, it is a good idea to always offer wet food, mixed with dry food, under or on it, very small portions and slightly warmed.
Grind up their favorite dry foo and sprinkle it over a small portion of wet food etc. Does the cat prefer fish over meat, or chicken over beef? Select the wet food accordingly. This accustoms the cat to the intake of wet food.