Depends on the type of stone. I was told to drink more water when I passed mine. It could be calcium build up, but it could be because of some other issue too. You'd have to take the stone in to have it properly analyzed to know for sure.
I just passed my second 1st right after my son 7 years ago! Then one Thursday (Nov 6th) I know there hereditary my moms had over 20! Not looking forward to anymore but unfortunately I don't think you can prevent them :( but I'm sure water will help decrease the risk I'm an advid soda drinker and I LOVE me some milk!!
Drink lemon water. The acid in the lemon helps break up stones especially if you have any extras lying around in there.