The main part of a rabbit's diet should be hay, preferably Timothy Hay, not alfalfa, then a good high fiber pellet, supplement the diet with greens such as basil, cilantro, carrot tops, parsley. You can also give a small amount of vegetables such as carrots, broccoli, or brussels sprouts. As a treat you can give a little bit of fruit such as a piece of apple, a couple of grapes or a slice of banana.
Remember that a rabbit's digestive system is very sensitive so introduce new foods slowly and in small amounts. Don't give veggies or fruit to rabbits under 4 months old.