At this early stage, it may be difficult to advise you on a suitable diet but this will be assessed in more detail after your tests.
Maintaining a high fluid intake (enough to keep your urine colourless) will reduce your risk of further stones. Water or squash are best; you can drink tea and coffee but in restricted amounts. There is some evidence that drinking the diluted juice of fresh lemons can reduce your risk of stones even further, by raising the levels of natural stone inhibitors in your urine.
For many years, conventional advice was always that you should avoid dairy produce (e.g. milk, butter, cheese & eggs). We now know that this is not desirable because it can, in fact, increase your risk of further stones. You should, however, reduce your intake of protein, salt and oxalate-containing foods and you should avoid Vitamin C or D supplements (including fish-oil preparations).
In summary, a normal-calcium, low-salt, low-protein diet can reduce your risk of stone formation by half. Keeping your urine colourless by increasing your fluid intake will reduce the risk by a further one third.
For more detailed advice on dietary recommendations, with examples of "stone-friendly" menus, click here to download an information leaflet (PDF) about stone prevention.