A lot of it is calories in and calories out. The best diet for you will likely balance high lean proteins rich in omegas with complex carbs. Fruits can be okay - especially the ones with low sugar content. Strawberries, blueberries, blackberries, etc. Keep in mind though, that, particularly while doing an exercise regimen, other fruits still have high nutritional value. Bananas and Oranges have potassium, which is key to lactic acid dispersion and muscle recovery.
To the point - I've never known anyone who got fat from eating too many raw fruits. Limit the soda and the fired shit and the pizza and stuff, and you'll be well on your way. It's easier if you stick to chicken, turkey, and fish or shrimp.