Kate - protein, fat and mainly green veg, and lots and lots of water. You should probably buy a copy of the Idiot Proof Diet guide by India and Neris which is very helpful and 'friendly' about the whole thing. And then the Briffa book is good on the science behind it (not too sciencey!)
Just to give you an idea, a typical day for me in the early weeks was:
Breakfast: Omelette with goats cheese, mushrooms and spinach
Lunch: Stir fried veg (peppers, cabbage, bean sprouts, broccoli with ginger, garlic and chilli) and prawns OR salad of chicken, avocado, bacon, parmesan, tomato, green beans, olives, spinach and dressing
Dinner: Salmon with creamy leeks and broccoli OR steak with stuffed mushroom and spinachy salad
Snacks if needed were a few lumps of cheese, slices of salami or some nuts, although I didn't always need a snack.