If I have calcium-oxalate kidney stones, what diet should I follow to prevent the formation of more stones?

It depends. There are several causes for calcium oxalate stones. If the problem is due to high calcium in your urine, about 50% of the time, limiting calcium intake will have an effect. If you have renal leak hypercalcuria, then diet changes won't help but thiazide medications will. Some people have hyper parathyroid disease and diet changes wont help.
Low oxalate diet. Avoid dehydration; Follow Diet: avoid spinach, rhubarb, strawberries, nuts, chocolate, tea, wheat bran, and all dry beans; increase Citrate: orange juice 8 oz twice daily; ReaLemon extract: 5 tblspns per day; increase fluid 4 liters/day; only 4 oz meat/day; 4-5 fruits/day; maintain low salt; egg white 2 per day as additional protein; 25 mg HCTZ (hydrochlorothiazide) daily to reduce Ca in urine - this will work;