Leafminers are difficult to control because they are protected inside the leaf. If you don't have a lot you can just pick off and destroy the affected leaves. If you want a pesticide treatment, spinosad may be worth a try (organic). It would help to know roughly whereabouts you are located.
Regarding nutrients, are you growing the tomatoes in the ground or in a pot? Do you have any idea of the nutrient status of your soil and your soil pH if the former? Have you grown tomatoes before and had problems?
